5.2 Quantitative Analysis (Edexcel GCSE Chemistry)

The balanced equation is:

H₂SO₄ + 2KOH → K₂SO₄ + 2H₂O

27.50 cm³ is 0.0275 dm³.

The ratio of acid to alkali is 1:3.

H₃PO₄ + 3NaOH → Na₂PO₄ + 3H₂O

The concentration in mol/dm³ of a solution of HCl with a volume of 23.55 cm³ and contains 0.00375 moles is:

Volume in dm³ = 0.02355 dm³

Concentration = = 0.16 mol/dm³

The four steps in a titration calculation are:

• Step 1: Write out the balanced equation for the reaction

• Step 2: Calculate the moles of the known solution given the volume and concentration

• Step 3: Use the equation to deduce the moles of the unknown solution

• Step 4: Use the moles and volume of the unknown solution to calculate the concentration

Using moles, volume in dm³ the equation is:

Concentration =

0.03905 dm³ is 39.05 cm³.

0.05 moles of HCl would be required as this reaction is a 1:1 ratio.

HCl + NaOH → NaCl + H₂O

Percentage yield compares the actual yield to the theoretical yield.

Actual yield is the recorded amount of product obtained from a chemical reaction.

The actual yield can be determined by experiment only.

Theoretical yield is the amount of product that would be obtained under perfect practical and chemical conditions.

The type of calculation lets you determine theoretical yield is a reacting mass calculation.

The equation for percentage yield is:

(actual yield theoretical yield) x 100

True.

For economic reasons, the objective is to have as high a percentage yield as possible to increase profits and reduce costs and waste.

If the actual yield is 1.50 g and theoretical yield is 2.00g, the percentage yield is:

(1.50 2.0) x 100 = 75%

Atom economy is a measure of the efficiency of a chemical reaction in terms of how well reactants are utilised to produce useful products.

Atom economy tells us what percentage of the mass of reactants become useful products.

To calculate atom economy:

Atom economy =

The atom economy for N₂ (g) + 3H₂ (g) ⇌ 2NH₃ (g) is 100% as there is only one product.

True.

The higher the atom economy of a process then the more sustainable that process is

The atom economy for the production of CaO in the reaction is 56%.

The atom economy of a reaction can be increased by selling the by-products of the reaction.

The atom economy for the production of ethene is 100%.

False.

Higher atom economy means less waste production.

Waste reduction in chemical processes is important because it minimises environmental impact and is more sustainable.

False.

Reactions with low atom economies are unsustainable and not economically attractive as they use up too much raw material and produce a lot of waste.

Three factors companies consider to improve efficiency are:

• Atom economy

• Percentage yield

• Rate of reaction

Percentage yield is the amount of product actually obtained from a reaction compared to the theoretical maximum amount, expressed as a percentage.

False.

Fast reaction rates are desirable attributes in industrial chemical processes.

Companies can improve the atom economy of a process by selling or reusing the waste products, or by considering alternative production methods with more useful by-products.

A reversible reaction is a chemical reaction that can proceed in both forward and backward directions, potentially reaching a state of equilibrium.

True.

Altering reaction conditions can shift the equilibrium position of a reversible reaction.

Waste disposal is expensive as it requires chemicals, equipment, space and transport.

A high temperature would favour the formation of products if the forward reaction is endothermic.

The equation for molar gas volume using moles and volume is:

Molar gas volume = volume / moles

The conditions for room temperature and pressure are:

• 20 ^oC

• 1 atmosphere

The equation to calculate moles using volume and molar gas volume is:

Moles = volume / molar gas volume

At rtp, the number of moles of gas present in 48 dm³ is:

• Moles = volume / molar gas volume

• Moles = 48 / 24 = 2

One mole of any gas at room temperature and pressure occupies:

• 24 dm³

• 24 000 cm³

The equation connecting moles, volume and molar gas volume is:

Volume = moles x molar gas volume

The amount of space, in dm³, that 1.5 moles of gas occupies is:

• Volume = moles x molar gas volume

• Volume = 1.5 x 24 = 36 dm³

True.

To convert volume from dm³ to cm³, you multiply by 1000.

A 300 dm³ cylinder contains 300 000 cm³ of gas.

True.

Avogadro’s Law states that equal amounts of gases occupy the same volume of space at the same temperature and pressure.

There are 2 moles of gas in 48 dm³.

moles = = 2

2.5 moles of gas will occupy 60 dm³ at RTP.

volume (dm³) = moles x 24

volume (dm³) = 2.5 x 24 = 60 dm³

The volume of ammonia is produced from 600 cm³ of hydrogen is 400 cm³.

N₂ (g) + 3H₂ (g)   2NH₃ (g)

hydrogen : ammonia = 3:2 ratio

volume of ammonia = 600 cm³ x = 400 cm³

If 250 cm³ of oxygen gas reacted reacted with propane, 150 cm³ of carbon dioxide is formed.

C₃H₈ (g) + 5O₂ (g) → 3CO₂ (g) + 4H₂O (g)

oxygen : carbon dioxide = 5:3 ratio

volume of carbon dioxide = 250 cm³ x = 150 cm³

100 cm³ of propane was required to react with 500 cm³ oxygen.

C₃H₈ (g) + 5O₂ (g) → 3CO₂ (g) + 4H₂O (g)

propane : oxygen = 1:5 ratio

volume of propane = = 100 cm³

The change in the number of moles of gas is 9 to 4 OR decreases by 5.

4NH₃ (g) + 5O₂ (g) → 4NO (g) + 6H₂O (l)