Answers to the C2 test you did in class

Answers to the C2 test you did in class here.

C1 test results

I hope you have all enjoyed your long weekend. This is just a quick post to say well done to D'marniea and Hashim who scored 96% in the C1 test! I hope you do as well in the real thing next week.

You can all check the mark scheme for this test by clicking the link below this post.
11b1 make sure you know the difference between atoms, particles and molecules. When explaining alloys you must talk about LAYERS OF ATOMS. Individual atoms don't 'move around' in a solid.

11a2 your C2 test is tomorrow. Good luck!

Answers to the C1 test you did in class

Find the questions and answers to the C1 test you did in class here

C1 Exam Questions with Answers

These are the questions we've practised in class with answers at the end.


Lime Cycle Q&A.rtf 
(See lime cycle blog post for diagram and notes)

Percentage oxygen experiments Q&A.rtf

Titration calculations examples

Thanks to Uwais and Shahzaib for these!
Titration calculation example answers.pdf

Revision Resources

Click here for lots of chemistry revision resources.

Tests

A reminder for next week's tests:
11a1 - C1 test on Friday
11b1 - C1 test on Friday
11a2 - C2 test on Tuesday

Make sure you revise!

Well done to Sulayman for the best marks on the C1 test in 11a2 this week - 91% to beat!

The scale of the Universe

This is just quite cool.
http://htwins.net/scale/

Titration Calculations

Click here for titration practice questions
Always follow the steps:

STEP 1: Write out a balanced equation for the neutralisation reaction.

STEP 2: Determine the ‘mole ratio’ between acid and alkali using the balanced equation.

STEP 3: Split the page into 2 sections and write in all the values (n, c, v) you know:

              ACID                                                                                    ALKALI

· You should have 2 values of the known solution and only 1 value for the unknown solution

· Remember to convert any volumes from cm³ into dm³ by dividing by 1000

STEP 4: Use the ‘mole ratio’ to find the value for N of the unknown solution.

 STEP 5: Use the triangle to complete the calculation now that you know 2 values for the unknown solution.

Lime Cycle

See your revision guide for the symbol equations.
Sometimes you will see this as 3 steps rather than 4 (all the water is added at once so you go straight from calcium oxide to calcium hydroxide solution).
This is quite often linked to a question about mass in a reaction. Remember, the total mass of the reactants = the total mass of the products.
It's usually a simple addition or subtraction but may need you to explain your answer.
Explanation: No atoms are lost or made in a chemical reaction; mass is always conserved.

Revision app

Revise on the go with this free app  http://www.gojimo.co/
Make sure you select Edexcel exam board!

Triple Science Bitesize page

A direct link to the triple science topics on the GCSE Bitesize site:

http://www.bbc.co.uk/schools/gcsebitesize/science/triple_edexcel/

Revision workbooks

If you haven't yet bought your revision workbooks you can still buy them through school for £4 and revision guides are £2.50. Well worth the investment!

Why not universal indicator?

You can't use universal indicator for titration because it doesn't give a single, sharp colour change. Simple as that. Nothing to do with time!

Why is it alkaline?

If the electrolysis of a solution (say, sodium chloride) produces a halogen gas (like chlorine), it doesn't produce oxygen. Therefore, hydroxide ions from the water remain in the solution. Lots of hydroxide ions means the solution is alkaline! See electrolysis notes below for more info.

Controlled Assessment

Great to see so many of you working hard after school today :) Come along again tomorrow for a shorter drop-in session from 2.30pm.

Controlled Assessment Session

Tomorrow 2.40-3.30pm. All triple scientists welcome to work on controlled assessment or quiet revision in 209.

11a1 homework

Homework reminder for 11a1 - C3 paper due Tuesday. If you need a new one collect a spare from 209 on Monday.

How to do a titration

https://www.youtube.com/watch?v=b3Im5IYtN_8

Coursework Catch up

Next coursework catch-up session Tuesday from 2.40pm to 3.30pm

Electrolysis Revision

Electrolysis

Electrolytes are ionic substances that are molten (melted) or dissolved in water.

During electrolysis, positively charged cations migrate to the negatively charged cathode and negatively charged anions migrate to the positively charged anode.

Oxidation means loss of electrons and reduction means gain of electrons.

Reduction occurs at the cathode and oxidation occurs at the anode.

A half equation shows the reaction at one electrode only. Electrons are shown by ‘e-’. For example:

Cu²⁺ + 2e^- à Cu

 

The full equation for the electrolysis of molten sodium chloride is NaCl à Na + Cl₂

The half equations are:

At the cathode: Na⁺ + e^- à Na

At the anode: 2Cl^- à Cl₂ + 2e^-

 

The electrolysis of solutions can give products from ions in water rather than from ions in the dissolved solid. We can predict the products of electrolysis using the following rules.

At the cathode:

·         If the metal is low in the reactivity series (e.g. copper, silver, lead), the metal is deposited on the cathode.

·         If the metal is high in the reactivity series (e.g. sodium, potassium), then hydrogen is given off.

At the anode:

·         If the non-metal in the sale is a halide ion (e.g. chloride, bromide, iodide), then the halogen (e.g. chlorine gas) is released.

·         If the non-metal is not a halogen, oxygen from the water is given off.

 

Sodium chloride solution is sodium chloride dissolved in water. The electrolysis of sodium chloride solution is: NaCl + 2H₂O à NaOH + Cl₂ + H₂.

In this case, hydrogen gas is formed at the cathode from the water instead of sodium. This is because hydrogen more easily gains an electron than sodium. Chlorine gas is formed at the anode. Na⁺ and OH^- ions are left in the water, and this means the solution is NaOH (sodium hydroxide).

 

Sodium and chlorine are both useful. Sodium is used in street lamps and as a coolant in some nuclear reactors. Chlorine is a toxic gas that can be used in disinfectants.

 

Write half equations for the electrolysis reactions for these ionic substances:

1.       Copper chloride solution CuCl₂

2.       Copper sulphate solution CuSO₄

3.       Sodium sulphate solution Na₂SO₄

4.       Molten lead bromide PbBr₂

 

Electrolysis is used for electroplating metals (adding a thin coating of one metal on the surface of another). This is useful because it can improve resistance to corrosion and improve the appearance of the metal.

 

Copper can be purified by electrolysis: the copper ions from the impure anode dissolve in the water and impurities sink to the bottom. The copper ions migrate to the pure copper cathode, so increasing its mass.