Principles of Chemistry

Define the term 'atom' and give an example.

Explain why elements in the same group (excluding Group 0) of the Periodic Table show similar chemical properties.

Helium and neon do not form any compounds. Using atomic structure, explain why the Group 0 elements are inert.

Describe a method the student could use to separate the sand from the salt in the mixture. Include the main steps and the name of each process.

After separation, the student makes a saturated solution of sodium chloride in 50 g of water at 20°C. She filters the solution to remove any excess solid, then evaporates the water and obtains 18.6 g of dry sodium chloride crystals.

Use these results to calculate the solubility of sodium chloride in water (in g per 100 g water) at 20°C.

In a different experiment, the student runs a paper chromatography investigation using three coloured inks from different pens. The chromatogram develops as shown below (all spots and the solvent front are marked by distance from the pencil line):

Calculate the R_f value for the green dye (Pen C).

Explain how a comparison of R_f values can help identify whether two pens use the same dye.

(i) A substance made of only one type of atom is called an _____.

(ii) A substance formed when two or more elements chemically combine is a _____.

(iii) A _____ contains different substances mixed together, not chemically joined.

(iv) The part of a solution that dissolves another substance is the _____.

(v) The dissolved solid in a solution is called the _____.

(vi) A _____ solution contains as much dissolved solute as possible at a particular temperature.

(vii) The _____ of a substance is the maximum mass that dissolves in 100 g of solvent at a specific temperature.

Outline an experiment to measure the solubility of a solid in water at 40°C. State the key steps and the measurements you would record.

The student measures the melting point of the powder. She finds that it melts over a range from 76°C to 83°C. Explain what this result suggests about the nature of the powder.

Describe how melting point measurements can be used to distinguish between a pure substance and a mixture. Give an example with data.

Describe the two separation techniques needed to obtain pure, dry potassium nitrate from the mixture.

The student adds the mixture to 40.0 g of water and stirs until no more potassium nitrate dissolves. After filtration, she evaporates the solution to recover 22.8 g of dry potassium nitrate. Calculate the solubility of potassium nitrate in water at this temperature (in g per 100 g water).

If the solubility of potassium nitrate at 60°C is 110 g per 100 g of water, and at 30°C it is 45 g per 100 g water, calculate the mass of potassium nitrate that will crystallise out when a saturated solution containing 110 g of potassium nitrate in 100 g water at 60°C is cooled to 30°C.

State why it is important to use filtration after dissolving the mixture in water.

Magnesium reacts with steam to produce magnesium oxide and hydrogen gas. Write a balanced chemical equation for this reaction, including state symbols.

Calculate the maximum volume, in cm³, of hydrogen gas formed at rtp when 3.60 g of magnesium is reacted with excess steam. (Ar: Mg = 24.0; molar volume at rtp = 24,000 cm³ mol⁻¹)

State one reason why the actual volume of hydrogen collected in an experiment might be less than your calculated answer.

Sodium carbonate decahydrate, Na2CO3·10H2O, is used in cleaning products. Calculate the relative formula mass (Mr) of sodium carbonate decahydrate. (Ar: Na = 23, C = 12, O = 16, H = 1)

A student dissolves 5.7 g of sodium carbonate decahydrate in enough water to make 250 cm³ of solution. Calculate the concentration of the solution in g/dm³.

Convert 250 cm³ to dm³. Show your working.

Define the mole in terms of the number of particles.

Recall the volume occupied by 1 mole of any gas at rtp in: (i) dm³ (ii) cm³

Calculate the total volume of gas (in cm³) produced at rtp when 5.35 g of ammonium chloride decomposes completely. (Ar: N = 14, H = 1, Cl = 35.5; molar volume = 24,000 cm³ mol⁻¹)

Write a balanced chemical equation (including state symbols) for the reaction between sodium carbonate and hydrochloric acid.

The student adds 0.0500 mol of sodium carbonate to 100 cm³ of 1.00 mol/dm³ hydrochloric acid. Calculate the number of moles of HCl present.

Explain which reactant is in excess, using calculations.

Calculate the volume (in dm³) of CO₂ produced at rtp. (Molar volume at rtp = 24 dm³ mol⁻¹)

Describe how magnesium and chlorine atoms form ions and the charges of these ions.

Explain what holds the ions together in the compound magnesium chloride.

Define a covalent bond and describe how it forms specifically in an ammonia (NH₃) molecule.

Compare the type of particles present in solid magnesium chloride and in ammonia. State one reason for your answer.

State whether you would expect solid magnesium chloride or ammonia to have a higher melting point. Explain your answer.