Chemical Calculations and Equations for A-Level Chemistry

What is the definition of a mole?

The mole is the amount of substance in grams that has the same number of particles as there are atoms in 12 grams of carbon-12.

What is Avogadro's Number?

Avogadro's Number is 6.022 x 10^23, which is the number of atoms in 12 grams of carbon-12.

What is relative atomic mass?

Relative atomic mass is the average mass of one atom compared to one twelfth of the mass of one atom of carbon-12.

What is relative molecular mass?

Relative molecular mass is the average mass of a molecule compared to one twelfth of the mass of one atom of carbon-12.

What is the equation for calculating moles from mass?

moles = mass / Mr (molar mass).

What is the equation for calculating moles from concentration and volume?

moles = concentration x volume.

What is the ideal gas equation?

PV = nRT, where P is pressure, V is volume, n is moles, R is the gas constant, and T is temperature.

What is the unit of pressure in the ideal gas equation?

The unit of pressure (P) is Pascal (Pa).

What is the unit of volume in the ideal gas equation?

The unit of volume (V) is cubic meters (m³).

How do you convert Celsius to Kelvin?

To convert Celsius to Kelvin, add 273.

What is an empirical formula?

An empirical formula is the simplest ratio of atoms of each element in a compound.

What is the general method for calculating an empirical formula?

1. Divide each mass (or % mass) by the atomic mass of the element. 2. Divide each result by the smallest number obtained. 3. Multiply to get whole numbers if necessary.

What is a molecular formula?

A molecular formula is the actual number of atoms of each element in a compound.

How do you determine the molecular formula from the empirical formula?

Divide the relative molecular mass (Mr) by the mass of the empirical formula to find how many times the empirical formula fits into the Mr.

What is a hydrated salt?

A hydrated salt contains water of crystallization.

What is the formula for density?

Density = mass / volume.

What is the unit of density typically used?

Density is usually given in grams per cubic centimeter (g cm⁻³).

How do you calculate the number of particles in a substance?

Number of particles = moles of substance (in mol) x Avogadro's constant.

What is the significance of significant figures in calculations?

Answers should be given to the same number of significant figures as the data provided in the question.

What is the molar mass of CaCO3?

The molar mass of CaCO3 is 100.1 g/mol (calculated as 40.1 + 12.0 + 16.0 x 3).

How do you convert cm³ to dm³?

To convert cm³ to dm³, divide by 1000.

What is the molar mass of water (H2O)?

The molar mass of water is 18.0 g/mol (2 x 1.0 for H + 16.0 for O).

What is the empirical formula for a compound containing 1.82g of K, 5.93g of I, and 2.24g of O?

The empirical formula is KIO3.

What happens to the mass of a hydrated salt when it is heated?

The mass decreases as water of crystallization is lost.

What is the molar mass of magnesium chloride (MgCl2)?

The molar mass of magnesium chloride is approximately 95.3 g/mol (24.3 for Mg + 2 x 35.5 for Cl).

If you have 0.400 mol dm⁻³ of MgCl2, how many moles of chloride ions are present?

There are 0.800 moles of chloride ions, as there are two chloride ions for every mole of MgCl2.

What is the formula to calculate the value of x in ZnSO4.xH2O?

Calculate the moles of ZnSO4 and H2O, then find the ratio.

How do you calculate the mass of H2O in the hydration of ZnSO4?

Mass of H2O = 3.51 g - 1.97 g = 1.54 g.

What is the molar concentration unit for solutions?

mol dm-3 or M.

How do you convert cm3 to dm3?

Divide by 1000.

What is the relationship between moles, mass, and molar mass?

moles = mass / Mr.

What happens when soluble ionic solids dissolve in water?

They dissociate into separate ions.

What is the concentration of a solution made by dissolving 5.00 g of Na2CO3 in 250 cm3 of water?

0.189 mol dm-3.

How do you calculate the concentration of a diluted solution?

Use the formula: original volume x original concentration = new diluted volume x new diluted concentration.

What units are used for pressure (P) in the ideal gas equation?

P is measured in Pascals (Pa).

How do you convert temperature from Celsius to Kelvin?

Add 273 to the Celsius temperature.

What is the molar gas constant (R) value?

R = 8.31 JK-1mol-1.

How do you calculate the mass of Cl2 gas using the ideal gas equation?

Use moles = PV/RT, then mass = moles x Mr.

What is the concentration of sodium ions when 5.86 g of NaCl is dissolved in 1 dm3 of water?

0.1 mol dm-3.

What is the concentration of chloride ions when 9.53 g of MgCl2 is dissolved in 1 dm3 of water?

0.2 mol dm-3.

What is the mass concentration unit?

g dm-3.

How do you convert concentration from mol dm-3 to g dm-3?

Multiply by the molar mass (Mr) of the substance.

What is the process for making a solution from a solid?

Weigh the solid, dissolve in water, and make up to the mark in a volumetric flask.

What is the dilution process using a volumetric pipette?

Pipette a specific volume of the original solution and dilute with distilled water.

What safety precautions should be taken when handling hazardous substances?

Wear goggles, gloves, and avoid skin contact.

What is the volume of water added to dilute 5.00 cm3 of 1.00 mol dm−3 hydrochloric acid to 0.050 mol dm−3?

95 cm3.

What is the relationship between original and diluted concentrations?

If moles do not change, original concentration x original volume = new diluted concentration x new diluted volume.

How do you calculate the volume of a gas using the ideal gas equation?

Use the equation PV = nRT and solve for volume (V).

What is the significance of the meniscus in volumetric measurements?

The bottom of the meniscus should sit on the line for accurate measurement.

What is the molar mass of Cl2 gas?

Cl2 = 35.5 x 2 = 71.0 g/mol.

What is the concentration of magnesium ions when 0.1 mol of MgCl2 is dissolved?

0.1 mol dm-3.

What are potential errors in using a gas syringe?

Gas escaping before bung is inserted, syringe sticking, and some gases being soluble in water.

How do you calculate the pressure of a gas mixture in a flask?

Use the equation P1V1 = P2V2.

What volume does 1 mole of any gas occupy at room temperature and pressure?

24 dm³

What is the relationship between equal volumes of gases at the same temperature and pressure?

They contain equal numbers of molecules.

In the reaction CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(l), what is the volume ratio of methane to oxygen?

1:2

What is the total volume of gases produced when 500 cm³ of CO reacts with 500 cm³ of NO?

750 cm³

How do you convert quantities between different substances using a balanced equation?

Use mole ratios from the balanced equation to convert moles of one substance to another.

What is the stoichiometric ratio in the reaction N2 + 3H2 → 2NH3?

1 mole of N2 reacts with 3 moles of H2 to produce 2 moles of NH3.

How do you calculate the mass of carbon dioxide produced from heating sodium hydrogencarbonate?

Use the balanced equation and the molar mass of CO2.

What is the formula for calculating percentage yield?

Percentage yield = (actual yield / theoretical yield) x 100.

What is the formula for calculating percentage atom economy?

Percentage atom economy = (mass of useful products / mass of all reactants) x 100.

What is the maximum mass of titanium produced from reacting TiCl4 with sodium?

Use the limiting reactant to calculate the mass of titanium formed.

What safety precautions should be taken during titrations?

Wear eye protection and gloves, rinse equipment properly, and treat unknown substances as potentially toxic.

What is the endpoint color change when using phenolphthalein as an indicator?

Pink (alkali) to colorless (acid).

What is the endpoint color change when using methyl orange as an indicator?

Yellow (alkali) to red (acid).

What happens if the jet space in the burette is not filled properly before a titration?

It can lead to errors in the titre reading.

How do you calculate the concentration of H2SO4 from a neutralization reaction with NaOH?

Use the moles of NaOH and the balanced equation to find moles of H2SO4, then calculate concentration.

What is the total volume of gas produced from heating magnesium nitrate?

Calculate using the balanced equation and the ideal gas law.

How do you calculate the moles of a substance from mass?

Moles = mass / molar mass (Mr).

What is the relationship between moles of HNO3 and Cu in the reaction 3Cu + 8HNO3?

8 moles of HNO3 react with 3 moles of Cu.

What is the molar volume of gas at standard conditions?

22.4 liters (or 22.4 dm³) at 0°C and 1 atm.

What is the ideal gas constant (R) in the ideal gas equation?

R = 8.31 J/(mol·K)

What is the significance of the limiting reactant in a chemical reaction?

It determines the maximum amount of product that can be formed.

How do you calculate the mass of a gas produced in a reaction?

Use moles of gas and multiply by the molar mass.

What is the effect of temperature on gas pressure?

Increasing temperature increases pressure if volume is constant.

What is the purpose of using a white tile under the flask during titration?

To help observe the color change.

How should acid be added to alkali during a titration?

Add acid dropwise at the end point while swirling the mixture.

What is the significance of obtaining concordant results in titration?

Concordant results are two readings within 0.1 cm³ of each other, indicating accuracy and consistency.

Why is a conical flask preferred over a beaker for titration?

It is easier to swirl the mixture without spilling.

What should be done if too much indicator is added during titration?

It can affect the titration result; only a few drops should be added.

How should results from a titration be recorded?

Results should be recorded in a table, including both initial and final readings, and titre volumes to 2 decimal places.

What is the role of distilled water during titration?

It washes the sides of the flask to ensure all acid reacts with the alkali.

What is the balanced equation for the reaction between acetic acid and sodium hydroxide?

CH3CO2H + NaOH → CH3CO2-Na+ + H2O.

What is the balanced equation for the reaction between sulfuric acid and sodium hydroxide?

H2SO4 + 2NaOH → Na2SO4 + 2H2O.

What is the equation for the reaction of hydrochloric acid with sodium bicarbonate?

NaHCO3 + HCl → NaCl + CO2 + H2O.

What is the purpose of quality control in titration?

To ensure the concentration of the chemical being tested is consistent across samples.

What substances are good for neutralizing excess acid?

Sodium hydrogen carbonate (NaHCO3) and calcium carbonate (CaCO3).

What is the first step in calculating the concentration of vinegar after titration?

Calculate the moles of sodium hydroxide used.

How do you calculate the moles of sodium hydroxide used in a titration?

Moles = concentration × volume.

What is the formula for calculating percentage error in apparatus?

% uncertainty = (±uncertainty / measurement made on apparatus) × 100.

What is the uncertainty of a reading using a burette?

±0.15 cm³.

How can you reduce uncertainties in titration?

Use more precise measuring equipment or increase the size of the measurement.

What is the maximum total percentage apparatus uncertainty?

It is the sum of all individual equipment uncertainties.

What is the significance of the percentage difference between actual and calculated values?

If the % uncertainty due to apparatus is greater than the percentage difference, the discrepancy is due to equipment sensitivity.

How do you calculate the mass of a substance using moles?

Mass = moles × molar mass.

What is the balanced equation for the reaction of calcium carbonate with hydrochloric acid?

CaCO3 + 2HCl → CaCl2 + CO2 + H2O.

What is the molar ratio of HCl to CaCO3 in the reaction?

2 moles of HCl react with 1 mole of CaCO3.

What is the molar ratio of NaOH to acetic acid in their reaction?

1 mole of NaOH reacts with 1 mole of acetic acid.

How do you determine the concentration of a diluted solution?

Concentration = moles / volume.