In I/GCSE Chemistry, we will learn about chemicals in analysis --- Stages and Sampling.
Stages in analysis
Qualitative: Type of chemicals present in sample
Quantitative: How much of each chemical is present in the sample
When it comes to I/GCSE Chemistry, Standard procedure = agreed method of working
- Safe -Effective-Accurate
- Sample taken (represents bulk material)
- Replicate samples ensure reliability --> find average
- Easier to analyse when chemicals are in liquid
- Accurately measure mass of samples and chemicals in it
- Find a property to measure e.g. how much acid is needed to neutralise the alkali
- Equation + conc. of acid is needed to find out --> volume of alkali needed to neutralise acid
- Compare values from replicate samples
- Closer values = more repeatable = more confidence
Sampling
Refer to I/GCSE Chemistry, Representative samples give an accurate reflection of the material as a whole
Homogenous – composition is uniform Heterogeneous – composition varies
Considerations
- No of samples + Mass of sample
- No of sample repeats (ensures reliability)
- Storage (prevents tampering with)
- Transport (prevents contamination)
Analysing water
Bottled water = homogenous b/c clear
- Single sample needed --> straightforward procedure
Stream water = heterogeneous b/c may be: cloudy; contain organisms; samples vary in different parts/ times of year.
- Lots of samples need to be stored --> complex procedure
Soil samples
Take the sample:
- Where there is a change in the soil
- Where you can’t see a change in the soil
- Anywhere there is a risk of damaged/contaminated soil
Sports sample
- Athletes pee in x2 bottles with witness watching to ensure no cheating
- Bottles are sealed and labelled with code (don’t want any influences if the name is revealed)
- Packaged in polystyrene
When it comes to I/GCSE Chemistry, One bottle analysed. The other is put in a freezer as backup.
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