Science - Chemical Analysis Homework

[ColyTom]

Science Homework.

I'm a bit stuck on some of the questions.
The ones I've already answered are in red.
There are a lot of questions so jsut help with the ones you can

25 - Sampling for analysis

Write down the main issues for the person plannign the analysis of the follow ing materials.

i) Soil in a farmers field.
It is hard to find a sample that will represent the bulk of the material.

ii) Water in a pond

iii) Polluted air in a city street

iv) Urine from an athlere.
They have to be sure that they have the right sample and that it has been correctly stored and labelled.

b) Give reason why it is important to have standard procedures for collecting storing and analysing samples.
I'm a bit stuck but is it because the samples may get mixed up?

26: Paper and thin layer chromatography.

a) Label this diagram it may help to use colours.


i) What would happen to a spot of substance on the start line that is not at all soluble in the mobile phase?
It would stay on the start line.

ii) Explain why sample Y moves further than sample X.
THe substance in sample Y is more soluble in the solution than sample X.

b) Complete this table to compare paper and thin-layer chromatography.
Paper Thin - Layer
Stationary phase
Mobile phase
Speed of seperation
Quality of seperation
Qualitative or quantitative?

27 - Interpreting Chromatograms

a) How many coloured chemicals were there in sample S? 3

b) Which permitted additives were present in the curry sauce? E102, E124

c) Calculate the Rf value for the spot that does not match any of the referebce colours.

Rf = Distance moved by spot
-------------------------
Distance moved by solvent front

d) Under the same conditions, the rf =0.15 for a banned colouring, Sudan 1. What does the chromatogram show us about the colourings in the curry sauce?

e) Suggest two ways which could be used to detect colourless additives on the chromatogram.

28 - Gas chromatography

All questions are diagram related.

a) Label this sequence of diagrams to shwo how you would prepare a solutino of sodum carbonates, Na2CO3, with a concentration of 10.6g/dm3, assumign that the volume of teh graduated flask is 250 cm3.

1) Accurately weigh ___ g of sodium carbonate.

2) Dissolve the solute in a small amont of water, warming it if necessary.

3) Transfer the solution to a 250 cm2 graduated flask.

4) Rinse all the solution into a flask with more _________________________.

5) Picture of something being put into the flask.

6) Picture of the flask.

B) A table I have done

C) A table I have done.

30 - Use of a pipette.

Suggest reasons for the following questions.

a) Have you rinsed the pipette with the solution you are going to measure out?

b) Have you made sure that there are no air bubbles in the narrower parts of the pipette?

c) Have you wiped out the pipette to remove solution on the outside of the glass before running out the liquid?

4) Have you liend up the meniscus with the graduation mark correctly?

31 - Use of a burette

Suggest reasons for the following questions.

a) Have you checked that the burette is clean before you start?

b) Have you rinsed the burette with the solution you are going to measure before filling it?

c) Have you read the burette correctly and taken both readings?

d) Have you left a drop hanging from the tip of the burette after runnign the solution into the flask?

32 - A titration to analyse vinegar

Diagram related questions

33 - Interpreting titration results

An analyst carried out a titration to find the concentration of limewater. Limewater is a saturated solution of calcium hydroxide, Ca(OH)2 in water. The analyst measured out 20.0cm3 sampels of limewater and then carried out titration with the dilute hydrochloric acid. The concentration of the acid was 1.46g/dm3 HCl(aq). The average titre was 25.0gm3 of the filute hydrochloric acid. Follow these steps to work out the concentration of calcium hydroxide in limewater.

a) Write the balanced equation.

b( Work out the formula masses of calcium hydroxide and hydrocholoric acid

(relative atomic masses: Ca =40, O = 16, H = 1, Cl = 35.5)

Ca(OH)2

HCl

C) Calculate the mass og HCl in the 25.0cm3 of the dilute hydrocholoric acid added from the burette.

d) Use the equation and the reacting masses to calculate the mass of calcium hydroxide that reacts with the HCl added from the burette.

e) This is the mass of calcium hydroxide in 20.0cm3 of limewater. Calculate the concentration of calcium hydroxide on limewater in g/dm3.

34 - Accurate quantitative analysis

Show how each stage applies to titration or explain how it is important

• Measuring out accurately a specified mass or volume of the sample
• Working with replicate samples
• Dissolving samples quantitatively
• Measuring a property of the o****ion quantatively
• Calculatign a vlaue for mthe measurements
• Estimating the degree on uncertainty in the reuslts

[Notex]

Lmao dude all the answers should be under the topic index.. thats what i found with assignments at school, the answers were right infront of us!

[ColyTom]

Lmao dude all the answers should be under the topic index.. thats what i found with assignments at school, the answers were right infront of us!

Yeah but my book is at school. I suppose I'll just have to do what I can.