Year 9 Science · Unit 2 · Lesson 20
Foundation Worksheet
Learning Goals
Fill the gap
Choose the correct word from the word bank. Two words will not be used.
The type of bonding in a material decides its properties. Salt, NaCl, has bonding: electrons move from one atom to another, and the ions form a rigid lattice with a high melting point. Inside a water molecule the atoms share electrons in bonds, and the weak forces between the molecules give water a low melting point. Metals are held together by bonding, a sea of free electrons, so they conduct electricity. When alkanes from crude oil undergo , they release energy, carbon dioxide and water. Alkene monomers can join to form a long-chain such as polyethylene. Crude oil is a resource: once it is used, it cannot be replaced. A material is if microorganisms can break it down into natural substances.
1. Name the property that tells you whether a material floats in water, and write the formula used to calculate it. Say what each letter stands for, with its unit.
Sort it
Write each item in the part of the unit it belongs to.
Bonding
Hydrocarbons
Polymers
Sustainability
Scenario: the life of a sea kayak
Many sea kayaks are made from polyethylene. Crude oil is the feedstock: the ethene for the plastic comes from cracking longer alkanes from crude oil. The ethene is polymerised, and the polyethylene powder is melted in a spinning mould to make a hollow kayak. After about 15 years in the sun, an old kayak turns brittle and small flakes break off.
2. A 20.0 cm³ offcut of the kayak’s plastic has a mass of 19.0 g. Calculate its density, and state whether the offcut floats in fresh water (1.00 g/cm³).
Density g/cm³
3. Decane is an alkane with 10 carbon atoms. Use CₙH₂ₙ₊₂ to write its formula. Then complete the cracking equation by filling in the missing product: C₁₀H₂₂ → C₈H₁₈ + ______
Read the data
If the old kayak is burned, its polyethylene reacts with oxygen. For each C₂H₄ unit: C₂H₄ + 3O₂ → 2CO₂ + 2H₂O. This means every 28 g of polyethylene makes 88 g of carbon dioxide.
| Polyethylene burned (kg) | Carbon dioxide made (kg) |
|---|---|
| 2.8 | 8.8 |
| 7.0 | 22 |
| 14 | |
| 21 |
Values worked out from the balanced equation and relative atomic masses.
4. Complete Table 1, showing your working for one row. The carbon dioxide made weighs more than three times as much as the plastic burned. Use the equation to explain where the extra mass comes from.
5. Polyethylene is a thermoplastic. Explain why grinding and remelting the old kayak to make new products is a better choice than burning it or sending it to landfill. Give two reasons.
6. Explain why the kayak turns brittle and flakes in the sun. Describe one way the flakes could harm sea life if the kayak is left on a beach.
7. Trace the polyethylene kayak through the unit’s framework: structure, bonding, properties, use and life cycle. Include at least one environmental consideration.