# EMPA A2 revision cards

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• Created by: chunks-42
• Created on: 06-05-16 16:43

## Titration Calculations

Assume the overall volume for titre 2 = 37.60cm3

Assume the volume for titre 1 = 23.80cm3

Assume the concentration of HCl = 0.1moldm-3

If the concentration of HCl is known then the moles of HCl can be determined. The ratio of HCl to hydrogencarbonate = 1:1 so the moles of hydrogencarbonate will be known. This is equal to the moles of carbonate.

Volume of HCl which reacts with HCO3- = 37.60 - 23.80 = 13.80cm3

Volume of HCl which reacts with CO32- = 13.80cm3

Volume of HCl which reacts with NaOH = 10.00cm3

2NaOH + CO2 --> Na2CO3 + H2O

Moles of HCl which reacts with Na2CO3 = 0.1 x 13.80/1000 = 0.00138

Moles of Hcl which reacts with NaOH = 0.1 x 10/1000 = 0.001

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## How to calibrate a pH meter

1. Submerse the electrode with buffers with known pH's.

2. Record the reading on the pH meter.

3. Plot a calibration curve of pH meter reading against actual pH.

4. Plot the results.

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## How to calculate the mass of CO2

2NaOH + CO2 --> Na2CO3 + H2O

V2 - V1 = Volume of HCl = NaHCO3 = Na2CO3 = CO2

Mass = moles x mr

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## EMF calculations

E cell = E right - E left

less negative - more positive

Zinc is able to reduce the Vanadium V down to Vanadium II. This is because the Eo value of Zn2+/Zn is lower than the Eo values of the vanadium

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## how to make a titration more accurate

1. use alkali in the burette instead of the acid

2. use a different indicator that won't go colourless

3. Ensure that the glassware is clean

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## Why do you use hot ethanol

To remove impurities in the filtrate

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## Why do you use a warm/hot filter

To avoid recrystalisation in the funnel

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## What is Solutions A, B, C and D and why?

Solution A = Vanadium, variable oxidation states

Solution B = Copper, blue precipitate redissolves in excess NH3 to royal blue solution

Solution C = Iron 2+, dark green precipitate that oxidises to orange-brown on standing with all added solutions

Solution D = Iron 3+, effervescence of CO2 on addition to Na2CO3

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## CuSO4 calculations

Might involve NH3

find out the number of moles of NH3

Find the ratio and find the mass/volume of copper sulphate

might be to find the percentage purity of copper sulphate made

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## Calculate the pH through pKa

pKa = -log Ka

pKa = Ka

H+ = shift log - pH

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## What is the half equivalence point

Half equivalence point = half of the value needed to neutralise the solution

Ka = [H+][A-]

[HA]

Only for the half equivalence point, Ka = [H+]

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