Chemistry questions, answered
Moles and molarity, pH and acids, dilution and concentration, reaction energy and the gas laws.
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Index Concentration Calculator NZ 2026/27
How concentrated is an index fund?
Far more than the holdings count suggests. On the worked example a fund holding 1,400 companies has 26.30% of its value in the largest ten, and behaves like roughly 107 equally weighted holdings rather than 1,400. The largest single position is 5.20% of the fund, which is 72.8 times what it would hold if every company were weighted equally.
What is the effective number of holdings?
The number of equally sized positions that would produce the same concentration as the fund actually has. It is calculated from a Herfindahl index, which is the sum of the squared weights, and it is the standard measure for this. On the worked example 1,400 stated holdings work out at about 107 effective ones, because weighting by company size means most of the money sits in a small number of names.
Is a fund with more holdings more diversified?
Not reliably. A fund holding 1,400 companies where the largest ten are 26.30% of the value is meaningfully less diversified than a fund holding 300 companies spread evenly. The count is the number most often quoted and the least informative of the measures available. The effective holdings figure answers the question the count is usually being used to answer.
What happens if the largest holdings fall?
The whole fund moves by the fall multiplied by their weight. On the worked example, a 20% fall confined to the top ten moves the fund 5.26% and takes $2,630.00 off a $50,000.00 holding, even if every other company in the index is flat. A 50% fall in those ten costs 13.15% of the fund, or $6,575.00.
Where do I find a fund's top ten holdings?
The monthly or quarterly factsheet, usually under a heading like top holdings or largest positions, alongside the total number of holdings. Every managed fund and exchange traded fund publishes one and it is free. The product disclosure statement describes the mandate rather than the current positions, so the factsheet is the better source.
Is concentration a reason to avoid index funds?
No, and that is not the argument here. A market-weighted index reflects what the market is actually worth, which is the point of it, and concentration rises and falls as markets do. The purpose of measuring it is so that the position is known rather than assumed, because an index fund is frequently bought on the belief that it removes single-company risk, and at these weights it reduces that risk rather than removing it.
How does the calculation handle the holdings I do not enter?
It spreads the remaining weight evenly across the remaining holdings. On the worked example that is 73.70% across 1,390 companies, an average of 0.0530% each. Real tails are not perfectly even, so the effective holdings figure is a slight overstatement of diversification, which means the true concentration is a little worse than reported here rather than better.
Does an equal weight fund fix this?
It addresses concentration directly, since every holding carries the same weight and the effective number of holdings equals the actual number. It brings its own trade-offs: higher turnover as the weights are reset, usually a higher fee, and a permanent tilt towards smaller companies. It is a different investment rather than a better-behaved version of the same one.
Acid Base Calculator
How do you find the pH of a weak acid?
For a weak monoprotic acid the hydrogen ion concentration is approximately the square root of the acid dissociation constant Ka multiplied by the concentration. The pH is then the negative base ten logarithm of that value. For 0.1 mol per litre acetic acid with a Ka of 1.8 times ten to the minus five, the pH works out to about 2.87.
What is the difference between a strong and a weak acid?
A strong acid dissociates completely in water, so the hydrogen ion concentration equals the acid concentration and the pH is just the negative log of the concentration. A weak acid only partly dissociates, so its hydrogen ion concentration is much lower and depends on its Ka. The same distinction applies to strong and weak bases with the hydroxide ion and Kb.
How are pH and pOH related?
In water at 25 degrees Celsius pH plus pOH always equals 14. So once you know one you know the other, and the hydrogen and hydroxide ion concentrations multiply to give the water constant of one times ten to the minus fourteen. A solution with a pH of 2.87 has a pOH of about 11.13.
Activation Energy Calculator
How do you calculate activation energy from two rate constants?
Use the two-point Arrhenius equation: Ea = R x ln(k2/k1) / (1/T1 - 1/T2), where R is the gas constant 8.314 J/(mol K) and T1 and T2 are absolute temperatures in kelvin. If a rate constant rises from 0.0025 to 0.035 between 300 K and 320 K, Ea = 8.314 x ln(14) / (1/300 - 1/320), which is about 105.3 kJ/mol.
What is activation energy?
Activation energy is the minimum energy colliding molecules need before a reaction can occur. It sets how strongly a reaction speeds up with temperature: reactions with a large activation energy are very temperature sensitive, while those with a small one change speed only modestly as the temperature rises.
What units should the temperatures and rate constants be in?
Temperatures must be absolute, in kelvin: add 273.15 to a Celsius temperature. The two rate constants can be in any units as long as both use the same units, because only their ratio enters the equation. The result comes out in joules per mole and is usually quoted in kilojoules per mole.
Atomic Mass Calculator
How do you calculate the average atomic mass of an element?
Multiply each isotope mass by its fractional abundance, then add the results. If abundances are given as percentages, divide the weighted total by the sum of the abundances. For chlorine, 34.96885 u at 75.77% and 36.96590 u at 24.23% give an average of about 35.45 u.
What is the difference between atomic mass and mass number?
The mass number is the whole number of protons plus neutrons in one atom of a specific isotope. The atomic mass shown on the periodic table is the weighted average mass of all naturally occurring isotopes, measured in unified atomic mass units (u), and is usually not a whole number.
What units is atomic mass measured in?
Atomic mass is measured in unified atomic mass units, written u or sometimes Da (dalton). One unified atomic mass unit is defined as one twelfth of the mass of a carbon-12 atom, which is why carbon-12 has a mass of exactly 12 u.
Beer-Lambert Absorbance Calculator
What is the Beer-Lambert law?
It states that absorbance equals molar absorptivity times concentration times path length. This means absorbance increases in proportion to how concentrated a solution is and how far light travels through it. It is the basis of quantitative spectroscopy.
How is transmittance related to absorbance?
Transmittance is the fraction of light passing through the sample and equals ten raised to the power of minus the absorbance. An absorbance of 1 means 10 percent of the light is transmitted. Higher absorbance means lower transmittance.
When does the law stop being accurate?
It is most accurate at low to moderate absorbance, up to around 1. At high concentrations the linear relationship can break down due to chemical and optical effects. Diluting the sample usually restores accuracy.
Beer-Lambert Law Calculator
What is the Beer-Lambert law?
Absorbance is proportional to concentration and path length: A = epsilon c l. It lets you find an unknown concentration from a measured absorbance.
What is molar absorptivity?
A constant, epsilon, that measures how strongly a substance absorbs light at a given wavelength, in litres per mole per centimetre.
When does the law break down?
At high concentrations and with scattering or chemical changes, the linear relationship can fail. It works best for dilute solutions.
Beer-Lambert Law Calculator NZ
What is the Beer-Lambert law?
It states that the absorbance of a solution equals the molar absorptivity times the path length times the concentration. Because absorbance is directly proportional to concentration, measuring it lets you determine an unknown concentration, the basis of spectrophotometric analysis.
How are absorbance and transmittance related?
Transmittance is the fraction of light that passes through, and it equals ten raised to minus the absorbance. So an absorbance of 1 means 10 percent transmittance, and an absorbance of 2 means 1 percent. As absorbance rises, transmittance falls steeply.
Why is path length usually 1 cm?
Standard laboratory cuvettes have a 1 centimetre path length, which makes absorbance directly proportional to the product of molar absorptivity and concentration. With a fixed path length, a calibration line of absorbance against concentration lets you read off unknowns easily.
Buffer pH Calculator
What is the Henderson-Hasselbalch equation?
The Henderson-Hasselbalch equation is pH = pKa + log([A-] / [HA]), where pKa is the negative base-10 logarithm of the acid dissociation constant, [A-] is the molar concentration of the conjugate base, and [HA] is the molar concentration of the weak acid. The equation approximates the pH of a buffer solution and is accurate when both concentrations are significantly greater than the hydrogen ion concentration (typically above 0.001 mol/L) and the ratio [A-]/[HA] is between 0.1 and 10.
What is the effective buffering range of a buffer solution?
A buffer solution resists pH change most effectively when the ratio of conjugate base to weak acid ([A-]/[HA]) is between 1:10 and 10:1. This corresponds to a pH range of pKa minus 1 to pKa plus 1. Outside this range, the buffer loses its ability to neutralise added acid or base, and the pH changes sharply. For maximum buffering capacity, choose a buffer whose pKa is as close as possible to the target pH.
How do I prepare a buffer at a specific pH?
To prepare a buffer at a target pH, first choose a weak acid whose pKa is within 1 unit of the target pH. Then use the rearranged Henderson-Hasselbalch equation to find the required ratio: [A-]/[HA] = 10^(pH - pKa). For example, to make an acetate buffer at pH 5.0 using acetic acid (pKa 4.76), you need [A-]/[HA] = 10^(5.0 - 4.76) = 10^0.24 = 1.74. So for every 1 mol/L of acetic acid, you need 1.74 mol/L of sodium acetate. Dissolve both in water and adjust with small amounts of acid or base to fine-tune the pH.
Combined Gas Law Calculator
What is the Combined Gas Law?
The Combined Gas Law merges Boyle's Law and Charles's Law into a single equation: P1 times V1 divided by T1 equals P2 times V2 divided by T2. It describes how a fixed amount of ideal gas behaves when pressure, volume, and temperature all change simultaneously. Unlike Boyle's Law (which requires constant temperature) or Charles's Law (which requires constant pressure), the Combined Gas Law applies to any change of state where the amount of gas remains constant.
How do you solve for V2 using the Combined Gas Law?
Rearrange P1V1/T1 = P2V2/T2 to isolate V2: V2 = (P1 times V1 times T2) divided by (T1 times P2). Substitute your known values to find V2. For example, P1=1 atm, V1=2 L, T1=300 K, P2=2 atm, T2=400 K gives V2 = (1 times 2 times 400) / (300 times 2) = 800/600 = 1.333 L.
What is the difference between the Combined Gas Law and the Ideal Gas Law?
The Combined Gas Law compares two states of the same fixed amount of gas (P1V1/T1 = P2V2/T2) without needing to know the number of moles. The Ideal Gas Law (PV = nRT) includes the number of moles n and the gas constant R, making it more general: it can find the absolute state of a gas rather than just comparing two states. If the amount of gas changes between states, you need the Ideal Gas Law, not the Combined Gas Law.
Combustion Reaction Calculator
How do you balance a combustion reaction?
For complete combustion of a hydrocarbon CxHy (or CxHyOz with oxygen already in the molecule), the balanced equation follows the formula: CxHyOz + (x + y/4 - z/2) O2 → x CO2 + (y/2) H2O. If the coefficient for O2 is not a whole number, multiply all coefficients by 2. For example, propane (C3H8): C3H8 + 5 O2 → 3 CO2 + 4 H2O. The number of moles of O2 needed is x + y/4 - z/2 per mole of fuel. Complete combustion assumes sufficient oxygen so that all carbon becomes CO2 and all hydrogen becomes H2O.
What is the heat released in combustion?
The heat released per mole of fuel burned is given by the standard enthalpy of combustion (delta H combustion), which is always negative (exothermic). It can be estimated from Hess's law using standard enthalpies of formation: delta H combustion = [x times delta Hf(CO2) + (y/2) times delta Hf(H2O)] - delta Hf(fuel). For common fuels: methane releases about 890 kJ/mol, propane about 2,220 kJ/mol, and octane about 5,471 kJ/mol. The heat released per gram of fuel is found by dividing the molar enthalpy by the molar mass of the fuel.
What is the difference between complete and incomplete combustion?
Complete combustion occurs when there is sufficient oxygen for all carbon atoms to form CO2 and all hydrogen atoms to form H2O. Incomplete combustion happens when oxygen is limited, producing carbon monoxide (CO), soot (unburned carbon), or other partially oxidised products alongside CO2 and H2O. Incomplete combustion releases less energy per mole of fuel and produces toxic CO. This calculator models complete combustion only. The stoichiometric air-fuel ratio represents the minimum oxygen needed for complete combustion.
Dilution Calculator (C1V1 = C2V2)
What does C1V1 = C2V2 mean?
C1V1 = C2V2 is the dilution equation, where C1 is the initial (stock) concentration, V1 is the initial volume you take from the stock, C2 is the final (desired) concentration after dilution, and V2 is the total final volume of the diluted solution. The equation comes from the conservation of moles: the number of moles of solute stays the same before and after adding the diluent (usually water). Rearranging the formula lets you solve for any one of the four variables given the other three.
How do I make a 10-fold dilution?
A 10-fold dilution (1:10) means the final solution is one-tenth the concentration of the original. To make it, take 1 part of your stock solution and add 9 parts diluent, giving a total of 10 parts. For example, take 1 mL of stock and add 9 mL of water to get 10 mL at one-tenth the original concentration. Using C1V1 = C2V2: if C1 = 1 mol/L and V2 = 10 mL, then C2 = 0.1 mol/L and V1 = 1 mL.
What units do I use in the dilution formula?
The units for concentration (C1 and C2) must match each other, and the units for volume (V1 and V2) must match each other. Common concentration units include mol/L (molarity), mg/mL, g/L, and percent (%). Common volume units include microlitres (uL), millilitres (mL), and litres (L). As long as both concentrations use the same unit and both volumes use the same unit, the equation works correctly. The result will be in whichever unit you are solving for.
Dilution Calculator
What is the dilution formula C1V1 = C2V2?
C1V1 = C2V2 states that the amount of solute before dilution equals the amount after. C1 is the initial (stock) concentration, V1 is the volume of stock used, C2 is the desired final concentration, and V2 is the total final volume. Rearranging: V1 = C2 x V2 / C1, which tells you how much stock to measure out.
How much diluent do I add?
The diluent (usually water) to add equals the final volume V2 minus the stock volume V1. For example, if V2 is 125 mL and V1 is 25 mL, you add 100 mL of water to 25 mL of stock to make up 125 mL total.
Do C1 and C2 have to be in mol/L?
No. Any consistent concentration unit works: mol/L, g/L, percent, or parts per million, as long as C1 and C2 use the same unit. Similarly, V1 and V2 can be in mL, L, or any other volume unit, as long as both use the same unit.
Dilution Ratio Calculator
What does a dilution ratio like 1:10 mean?
A dilution ratio of 1:10 means 1 part concentrate to 10 parts water, making 11 total parts. So for every 1 unit of concentrate, you add 10 units of water. Some manufacturers use a different convention where 1:10 means 1 part concentrate mixed into a total of 10 parts (1 part concentrate plus 9 parts water). Always check the product label to see which convention it uses, since this affects the final strength significantly.
How do I convert a dilution ratio to a percentage?
Divide the concentrate parts by the total parts and multiply by 100. For a 1:10 ratio (1 part concentrate to 10 parts water, 11 parts total), the strength is 1 divided by 11, which is approximately 9.1 percent concentrate. For a 1:4 ratio (5 total parts), the strength is 1 divided by 5, which is 20 percent.
How much concentrate do I need for a specific bottle size?
Divide your target total volume by the total number of parts in the ratio, then multiply by the concentrate parts. For a 1:32 ratio and a 1000 mL spray bottle, there are 33 total parts, so each part is 1000 divided by 33, which is about 30.3 mL. The concentrate needed is 1 part, or about 30.3 mL, topped up with roughly 969.7 mL of water.
DNA Concentration Calculator
How do you calculate DNA concentration from A260?
DNA concentration (ng/uL) equals the A260 absorbance reading multiplied by the extinction coefficient for double-stranded DNA (50 ng/uL per A260 unit) multiplied by the dilution factor used in the cuvette. For example, an A260 of 0.400 measured neat (dilution factor of 1) gives a concentration of 0.400 x 50 x 1 = 20 ng/uL. If the sample was diluted 10-fold before measuring, multiply by 10 for a result of 200 ng/uL.
What A260/A280 ratio indicates pure DNA?
A A260/A280 ratio of approximately 1.8 indicates relatively pure double-stranded DNA. A lower ratio (below 1.7) suggests contamination with protein or phenol, while a higher ratio (above 2.0) may indicate RNA contamination. These are guidelines rather than strict cutoffs, since the ratio is also sensitive to buffer pH and low sample concentrations, but 1.8 is the widely used benchmark for a clean genomic DNA prep.
How do I calculate the dilution needed for a target DNA concentration?
Use the dilution formula C1V1 = C2V2, where C1 is your stock concentration, V1 is the volume of stock to use, C2 is your target concentration, and V2 is your final total volume. Rearranged, V1 = (C2 x V2) / C1. For example, to make 50 uL of a 10 ng/uL working stock from a 200 ng/uL sample, V1 = (10 x 50) / 200 = 2.5 uL of stock, topped up with 47.5 uL of diluent (usually TE buffer or nuclease-free water).
Enthalpy Calculator
What is the formula for enthalpy change?
For sensible heat (temperature change without phase change), the enthalpy change is calculated as delta H = m times c times delta T, where m is mass in kilograms, c is the specific heat capacity in joules per kilogram per kelvin (J/kg/K), and delta T is the change in temperature in kelvin or degrees Celsius. A positive delta T means heat is absorbed (endothermic); a negative delta T means heat is released (exothermic).
What is the specific heat capacity of water?
The specific heat capacity of liquid water is approximately 4184 J/kg/K (often rounded to 4200 J/kg/K). This is unusually high compared with most other substances, which is why water is such an effective coolant and why large bodies of water moderate climate. By comparison, iron is about 449 J/kg/K and aluminium is about 900 J/kg/K.
What is the difference between endothermic and exothermic?
An endothermic process absorbs heat from the surroundings, so the system gains energy and delta H is positive. An exothermic process releases heat to the surroundings, so the system loses energy and delta H is negative. Combustion, rusting, and neutralisation reactions are typically exothermic. Dissolving ammonium nitrate in water and photosynthesis are endothermic examples.
Enthalpy Change Calculator
What is enthalpy change?
Enthalpy change is the heat absorbed or released by a reaction at constant pressure. A negative value means the reaction is exothermic and gives out heat; a positive value means it is endothermic and takes heat in. It is usually quoted in kilojoules per mole.
How do you calculate enthalpy change from calorimetry?
First find the heat using q equals mass times specific heat capacity times the temperature change. Then divide by the number of moles reacting and change the sign, since a temperature rise means the reaction released heat. The result is the enthalpy change per mole.
Why is the sign reversed?
In a calorimetry experiment, a temperature rise means heat flowed into the surroundings, so the reaction lost energy and its enthalpy change is negative. The heat calculated from the solution warming up is therefore given the opposite sign to get the reaction enthalpy.
Enthalpy of Reaction Calculator
How do I find reaction enthalpy from formation data?
Sum the formation enthalpies of the products, subtract the sum for the reactants, weighting each by its coefficient.
What is the formation enthalpy of an element?
Zero, for an element in its standard state, by definition.
Why products minus reactants?
It follows from Hess’s law: forming products from elements, and un-forming reactants back to elements, gives the overall change.
Half-Life Calculator
What is a half-life?
A half-life is the time it takes for half of a quantity to decay or disappear. After one half-life, 50% remains; after two half-lives, 25% remains; after three, 12.5%, and so on. The quantity follows an exponential curve that approaches but never quite reaches zero.
What is the half-life formula?
The amount remaining is N(t) = N0 x (1/2)^(t / t_half), where N0 is the starting amount, t is the elapsed time, and t_half is the half-life. The exponent t / t_half gives the number of half-lives that have passed.
What is the half-life of carbon-14?
Carbon-14 has a half-life of approximately 5,730 years. This means that after 5,730 years, half of the original carbon-14 in a sample has decayed to nitrogen-14. After 11,460 years (two half-lives), only one quarter (25%) of the original amount remains, which is the default worked example in this calculator.
Ideal Gas Density Calculator
What units should I use for this calculator?
Use pascals for pressure, kilograms per mole for molar mass and kelvin for temperature. These SI units give the density directly in kilograms per cubic metre. Convert degrees Celsius to kelvin by adding 273.15.
Where does density equals PM over RT come from?
It comes from the ideal gas law PV equals nRT. Replacing the number of moles with mass divided by molar mass and rearranging for mass over volume gives density equals pressure times molar mass over the gas constant times temperature.
How accurate is the ideal gas assumption?
It is very good for gases at low pressure and ordinary or high temperature. Real gases deviate near their condensation point or at very high pressure. For everyday air at room temperature the estimate is reliable.
Ideal Gas Law Calculator
What is the ideal gas law?
The ideal gas law is PV = nRT, where P is pressure, V is volume in litres, n is the number of moles of gas, R is the universal gas constant, and T is absolute temperature in kelvin. It describes the behaviour of a hypothetical ideal gas whose molecules occupy no volume and experience no intermolecular forces.
How do I convert Celsius to kelvin for the ideal gas law?
Add 273.15 to the Celsius temperature. For example, 0 degrees C is 273.15 K, 25 degrees C is 298.15 K, and 100 degrees C is 373.15 K. The ideal gas law requires absolute temperature in kelvin; using a Celsius value directly will give a wrong answer.
What volume does one mole of gas occupy at STP?
At standard temperature and pressure (0 degrees C and 1 atm), one mole of an ideal gas occupies 22.414 litres. This molar volume arises directly from PV = nRT when you substitute P = 1 atm, n = 1 mol, and T = 273.15 K using R = 0.08206 L atm per mol per K.
Molar Mass Calculator
What is molar mass?
Molar mass is the mass of one mole of a substance, expressed in grams per mole (g/mol). It is numerically equal to the molecular weight in atomic mass units and is calculated by summing the standard atomic weights of every atom in the chemical formula.
How do I enter a chemical formula correctly?
Use the correct capitalisation for element symbols: a capital first letter and a lower-case second letter where applicable, such as Na, Cl, Ca, or Mg. Write subscript numbers as ordinary digits, as in H2O or C6H12O6. Brackets are supported for grouped units, so ammonium sulfate is (NH4)2SO4 and aluminium sulfate is Al2(SO4)3.
What is the molar mass of water (H2O)?
Water (H2O) has a molar mass of 18.02 g/mol. It is calculated by adding the atomic weight of two hydrogen atoms (2 x 1.008 = 2.016) plus one oxygen atom (15.999), giving 18.015 g/mol, rounded to 18.02 g/mol.
Molarity Calculator
What is molarity?
Molarity is the concentration of a solution, measured as moles of solute per litre of solution (mol/L or M). A 2 M solution contains 2 moles of dissolved substance in every litre of solution. Molarity is the most widely used concentration measure in chemistry.
What is the molarity formula?
Molarity (M) equals moles of solute (n) divided by volume of solution in litres (V): M = n / V. Rearranged: moles equals molarity times volume (n = M x V), and volume equals moles divided by molarity (V = n / M).
How do I convert millilitres to litres for the molarity formula?
Divide the volume in millilitres by 1000 to get litres. For example, 250 mL is 0.25 L. The molarity formula requires volume in litres, so always convert before entering the value.
Mole to Mass Calculator NZ
How do I convert moles to mass?
Multiply the number of moles by the molar mass of the substance in grams per mole. For example, 2 moles of water at 18.015 grams per mole is 36.03 grams. To go from mass to moles, divide the mass by the molar mass instead.
What is molar mass?
It is the mass of one mole of a substance, in grams per mole, equal to its relative atomic or molecular mass. You find it by adding the atomic masses of all the atoms in the formula, using values from the periodic table.
How many particles are in a mole?
One mole contains Avogadro's number of particles, about 6.022 times ten to the twenty-three. So multiplying the number of moles by this gives the number of atoms or molecules, the bridge between counting particles and weighing a measurable mass.
Moles Calculator (Mass to Moles)
How do you calculate moles from mass?
Use the formula n = m / M, where n is moles, m is mass in grams, and M is molar mass in grams per mole (g/mol). For example, 36.03 g of water (molar mass 18.015 g/mol) gives 36.03 / 18.015 = 2.000 mol. The molar mass of an element or compound is found by summing the atomic masses from the periodic table for each atom in the formula.
How do you find the molar mass of a compound?
Add the atomic masses (from the periodic table) of every atom in the chemical formula. For water (H2O): 2 x 1.008 (hydrogen) + 1 x 15.999 (oxygen) = 18.015 g/mol. For sodium chloride (NaCl): 22.990 (Na) + 35.45 (Cl) = 58.44 g/mol. For glucose (C6H12O6): 6 x 12.011 + 12 x 1.008 + 6 x 15.999 = 180.156 g/mol.
How many molecules are in one mole?
One mole contains exactly 6.02214076 x 10^23 particles (atoms, molecules, or formula units). This is Avogadro's number (N_A). So if you have 2 moles of water, you have 2 x 6.022 x 10^23 = 1.204 x 10^24 water molecules. Multiply moles by Avogadro's number to find the number of particles.
Moles Calculator
What is a mole in chemistry?
A mole is the SI unit for amount of substance. One mole contains exactly 6.022 x 10^23 particles (Avogadro's number). The mass of one mole of a substance in grams is its molar mass, which is numerically the same as its molecular weight in atomic mass units.
What is the moles formula?
Moles (n) equals mass in grams (m) divided by molar mass in grams per mole (M): n = m / M. Rearranged: mass equals moles times molar mass (m = n x M), and molar mass equals mass divided by moles (M = m / n).
How many moles are in 18 grams of water?
Water (H2O) has a molar mass of 18.02 g/mol. Dividing 18 grams by 18.02 g/mol gives approximately 1.00 mole. This matches the default worked example in the calculator.
pH Calculator
What is pH?
pH is a measure of the acidity or alkalinity of a solution. It is defined as the negative base-10 logarithm of the hydrogen ion concentration in moles per litre: pH = -log10([H+]). The scale typically runs from 0 (strongly acidic) through 7 (neutral) to 14 (strongly alkaline), though values outside this range are possible.
How are pH and pOH related?
At 25 degrees Celsius, pH plus pOH equals 14. This comes from the water dissociation constant Kw = [H+][OH-] = 1 x 10^-14. So if pH is 3, pOH is 11, and if pH is 11, pOH is 3.
What [H+] concentration gives a pH of 3?
A pH of 3 corresponds to a hydrogen ion concentration of 10^-3 mol/L, which is 0.001 mol/L. This is the default worked example in the calculator. Each whole number step on the pH scale represents a tenfold change in hydrogen ion concentration.
pH and pOH Calculator
What does pH actually measure?
pH measures how acidic or alkaline a solution is on a logarithmic scale. It is the negative base ten logarithm of the hydrogen ion concentration in moles per litre. Each whole pH unit represents a tenfold change in acidity.
Why does pH plus pOH equal 14?
At 25 degrees Celsius the ion product of water is ten to the power minus 14. Taking logarithms of that relationship gives pH plus pOH equal to 14. This holds at room temperature but shifts slightly at other temperatures.
What pH counts as neutral?
At 25 degrees Celsius pure water has a pH of 7, which is neutral. Below 7 is acidic and above 7 is alkaline. At higher temperatures neutral pH is slightly lower than 7.
ppm Concentration Calculator
What is parts per million?
Parts per million, or ppm, is a way of expressing a very small concentration as the number of parts of solute for every million parts of solution. It equals the amount of solute divided by the amount of solution, multiplied by one million.
How do you convert ppm to a percentage?
Divide the ppm value by 10,000. So 500 ppm is 500 divided by 10,000, which is 0.05 percent. Going the other way, multiply a percentage by 10,000 to get ppm.
Is ppm the same as mg per litre?
For dilute solutions in water, yes, near enough. Because a litre of water weighs about one kilogram, 1 mg of solute per litre is about 1 mg per kilogram, which is 1 ppm. This is why water quality results are often given in both mg per litre and ppm.
Rate Constant (Arrhenius) Calculator
What is the Arrhenius equation?
The Arrhenius equation is k = A · exp(-Ea / (R · T)), where k is the rate constant, A is the pre-exponential (frequency) factor, Ea is the activation energy in J/mol, R is the universal gas constant (8.314 J/mol·K), and T is the absolute temperature in Kelvin. It describes how the rate of a chemical reaction depends on temperature: higher temperatures give larger k values, meaning faster reactions. The equation was proposed by Svante Arrhenius in 1889.
How do I convert activation energy from kJ/mol to J/mol?
Multiply the value in kJ/mol by 1,000 to get J/mol. For example, an activation energy of 75 kJ/mol equals 75,000 J/mol. This is necessary because the gas constant R = 8.314 J/(mol·K) uses joules, not kilojoules. This calculator accepts both units: select kJ/mol from the dropdown and the conversion is applied automatically.
What does the pre-exponential factor A represent?
The pre-exponential factor A (also called the frequency factor or collision frequency) represents the maximum possible rate constant if every collision between reactant molecules led to a reaction, regardless of orientation or energy. Its units match those of k: for a first-order reaction, A is in s⁻¹; for a second-order reaction, A is in L/(mol·s). A accounts for the frequency of collisions and the fraction of molecules that have the correct orientation to react. Typical values range from about 10^10 to 10^13 s⁻¹ for gas-phase reactions.
Stoichiometry Calculator
What is stoichiometry?
Stoichiometry is the branch of chemistry that deals with the quantitative relationships between reactants and products in a chemical reaction. It uses the mole ratios from a balanced equation to convert between masses of different substances involved in the reaction.
How do you do a mass to mass stoichiometry calculation?
Four steps: 1. Convert the mass of the given substance to moles by dividing by its molar mass. 2. Multiply by the mole ratio (moles of wanted substance per mole of given substance from the balanced equation). 3. Multiply by the molar mass of the wanted substance to get grams. Written as one formula: mass_wanted = mass_given / MM_given x ratio x MM_wanted.
What is a mole ratio in stoichiometry?
The mole ratio is the coefficient of the wanted substance divided by the coefficient of the given substance in the balanced chemical equation. For 2H2 + O2 gives 2H2O, the ratio of H2O to H2 is 2/2 = 1, while the ratio of O2 to H2 is 1/2 = 0.5.
Titration Calculator NZ
How do you find concentration from a titration?
At the equivalence point, work out the moles of titrant from its concentration and volume, multiply by the mole ratio from the balanced equation to get the moles of analyte, then divide by the analyte volume. This calculator does each step for you.
What is the mole ratio?
It is the ratio of analyte to titrant in which they react, read from the balanced equation. For a one-to-one reaction it is 1. For a diprotic acid reacting with a base it would be 1 to 2, so set the analyte-to-titrant ratio accordingly to get the right concentration.
Do the volumes need to be in litres?
You can enter the volumes in millilitres, since they appear as a ratio in the final calculation and the units cancel. Just keep both volumes in the same unit. The titrant concentration should be in moles per litre, and the result is the analyte concentration in moles per litre.
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Answers are gathered from the calculators and guides listed above and are general information, not advice. Last reviewed 2026-09-06. See also the finance glossary, the guides and the reference data.