Revision Topic 1 chemistry

Revision DP2 chemistry

Topic 1,4,9,10

Topic 1 - stoichiometry

You need to use various formulae but all of them are around mole.

A mole is a concept used in chemistry that is equal to 6.02 *10²³ of particles.

Formulae you need to know:

n=N/N_A, n=m/M, n=V/Vm, n=C*V, yield=m_actual/m_theoretical,

mass%=(m_substance/m_total)*100

PV=nRT - is given in the booklet

How do you solve a problem?

1 Realise what you were given

2 Calculate what can be calculated

3 Find a way to the value that is needed to be calculated (usually you have 1 or 2 step questions only, the multi-step processes are divided into smaller questions)

The question asks to calculate molar concentration which is C=n/V

V is given 500 cm³ . n is missing. we also have 0.200 g the mass of lithium. We know that there is n=m/M formula. It is the only thing we can do with the mass, hence n(Li)=0.200/6.94=0.0288 mol

Now that we have the mole we can use the equation and see that the mole of Li is equal to the mole of LiOH (same ratio) meaning that n(Li)=n(LiOH)

C(LiOH)=0.0288/0.500=0.0576 mol dm^-3 is the answer

Example

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Question 1

5.00 g of an impure sample of hydrated ethanedioic acid, (COOH)₂•2H₂O, was dissolved in water to make 1.00 dm³ of solution. 25.0 cm³ samples of this solution were titrated against a 0.100moldm^-3 solution of sodium hydroxide using a suitable indicator.

(COOH)₂ (aq) + 2NaOH (aq) → (COONa)₂ (aq) + 2H₂O (l)

Fill in the Blanks

Calculate the amount, in mol, of NaOH in 14.0cm³ of 0.100moldm^-3 solution.

Fill in the Blanks

Calculate the amount, in mol, of ethanedioic acid in each 25.0 cm³ sample.

Fill in the Blanks

Determine the percentage purity of the hydrated ethanedioic acid sample.

Question 2

2.478 g of white phosphorus was used to make phosphine according to the equation:

P₄(s)+3OH⁻(aq)+3H₂O(l)→PH₃(g)+3H₂PO₂⁻(aq)

Fill in the Blanks

2.478 g of white phosphorus was used to make phosphine according to the equation:

P₄(s)+3OH⁻(aq)+3H₂O(l)→PH₃(g)+3H₂PO₂⁻(aq)

Calculate the amount, in mol, of white phosphorus used.

Fill in the Blanks

2.478 g of white phosphorus was used to make phosphine according to the equation:

P₄(s)+3OH⁻(aq)+3H₂O(l)→PH₃(g)+3H₂PO₂⁻(aq)

This phosphorus was reacted with 100.0cm³ of 5.00mol dm⁻³ aqueous sodium

hydroxide. Deduce, showing your working, which was the limiting reagent.

Fill in the Blanks

2.478 g of white phosphorus was used to make phosphine according to the equation:

P₄(s)+3OH⁻(aq)+3H₂O(l)→PH₃(g)+3H₂PO₂⁻(aq)

This phosphorus was reacted with 100.0cm³ of 5.00mol dm⁻³ aqueous sodium

hydroxide. Deduce, showing your working, which was the limiting reagent.

Determine the excess amount, in mol, of the other reagent.

Fill in the Blanks

2.478 g of white phosphorus was used to make phosphine according to the equation:

P₄(s)+3OH⁻(aq)+3H₂O(l)→PH₃(g)+3H₂PO₂⁻(aq)

Determine the volume of phosphine, measured in cm³ at standard temperature and pressure, that was produced.

Fill in the Blanks

Question 3

The oxide formed in the reaction with air contains 43.6 % phosphorus by mass. Determine the empirical formula of the oxide, showing your method.

Fill in the Blanks

Question 4

Calculate the number of hydrogen atoms in 1.00 g of propan-2-ol.

Question 5

3.26 g of iron powder are added to 80.0 cm³ of 0.200 mol dm⁻³ copper(II) sulfate solution. The following reaction occurs:

Fe (s) + CuSO₄ (aq) → FeSO₄ (aq) + Cu (s)

Fill in the Blanks

Determine the limiting reactant showing your working.

Fill in the Blanks

The mass of copper obtained experimentally was 0.872 g. Calculate the percentage yield of copper.

Question 6

When heated in air, magnesium ribbon reacts with oxygen to form magnesium oxide.

The reaction was carried out in a crucible with a lid and the following data was recorded:

Mass of crucible and lid = 47.372 ±0.001 g

Mass of crucible, lid and magnesium ribbon before heating = 53.726 ±0.001 g

Mass of crucible, lid and product after heating = 56.941 ±0.001 g

Fill in the Blanks

Calculate the amount of magnesium, in mol, that was used.

Fill in the Blanks

Determine the percentage uncertainty of the mass of product after heating.

Fill in the Blanks

Assume the reaction is the only one occurring and it goes to completion, but some product has been lost from the crucible. Deduce the percentage yield of magnesium oxide in the crucible.