Unit 3- Area of Study 1: Chemical Analysis Flashcards
Define relative atomic mass.
The weighted mean of the relative isotopic masses of an element on the scale where carbon-12 is 12 exactly. (Symbol:Ar)
Define relative molecular mass.
The relative mass of a molecule on the scale where carbon-12 is 12 exactly. It is equal to the sum of the relative atomic masses of the atoms in the molecule. (Symbol: Mr)
Define mole.
The amount of substance that contains the same number if fundamental particles as there are atoms in 12g of carbon-12. (Symbol:n)
Define Avogadro’s number.
Number of particles in a mole; 6.02 X 10^23 (Symbol: NA)
Define molar mass.
The mass of one mole of a substance. It is equal to the relative mass of the substance expressed in grams. (Symbol: M)
Define precipitate.
A solid formed during a reaction in which two or more solutions are mixed.
What is gravimetric analysis?
A quantitative analytical technique which is based on the mass of a substance and involves precipitation and weighing.
What is an ionic equation?
An equation that contains only the ions that are involved in the reaction.
What us the instrument used in gravimetric analysis?
An analytical balance scale.
What are the advantages of using an analytical balance scale as opposed to a regular scale?
- There is no contamination of the sample.
- Environmental factors don’t affect the mass of sample.
- An accurate measurement up to 4 decimal places is given.
In what situations is gravimetric analysis used?
1) Measuring water content in the sample.
2) Determining the composition in a mixture.
3) Determining the chemical formula of a compound.
What are the steps involved in measuring the water content in a sample?
1) Weigh the sample (M1 g-initial mass)
2) Heat the sample in an oven at 110 deg cel. *Never measure a sample when it is hot because as the temp is increased, pressure is increased and this affects the mass to 4 d.p. *
3) Allow sample to cool in a dessicator
4) Reweigh the sample (M2 g- final mas)
5) Repeat steps 2-4 until final mass is constant.
Define empirical formula.
The simplest whole number mole ratio of elements in one mole of a compound.
Define molecular formula.
The exact whole number mole ratio of elements in one mole of a compound.
List the various analytical techniques used for chemical analysis.
- Gravimetric analysis
- Volumetric Analysis
- Chromatographic analysis
- Spectroscopic tecnhique
- Mass spectrometry
The two main categories of chemical analysis.
- Qualitative analysis
* Quantitative analysis
Define qualitative analysis.
The process of finding what chemicals are present in the substance.
Define quantitative analysis.
The process of finding how much of each chemical is present in the substance,
What are the experimental steps required to calculate the NaCl% in a soup sample?
1) Weigh the soup sample (m1 g- initial mass)
2) Add an EXCESS of AgNO3 solution to precipitate Cl- ions as AgCl.
3) Filter the AgCl precipitate using a vacuum filter.
4) Wash the precipitate with a small amount of water in order to wash away/remove water soluble impurities.
5) Dry the precipitate in an oven at 110 deg cel.
6) Allow the precipitate to cool in a dessicator.
7) Reweigh the precipitate.
8) Repeat steps of heating until final mass is constant (m2 g)
9) Convert the mass of AgCL into moles. Use this to find out number of moles of NaCl and hence the mass of it.
10) Calculate the percentage composition of NaCl.
What are the ccombinations of ions that make good precipitates for use in gravimetric analysis?
*Cl-/ Br-/I- AND Ag+/Pb2+ AND BaSO4
AgCl, AgBr, AgI, PbCl2, PbBr2, PbI2, BaSO4
What ions (in compounds) are always soluble?
Remember: SNAPE Sodium, Nitrate, Ammonium, Potassium, Ethanoate.
What are the properties of a primary standard solution?
- be readily obtainable in a pure form
- have a known formula
- be easy to store without deteriorating or reacting with the atmosphere
- have a high molar mass to minimise the effect of errors in weighing
- be cheap (inexpensive)
What are the two types of standard solutions?
1) Primary standard solution
2) Secondary standard solution
During the preparation of the standard solution shown in Figure 3.4, why is water added to the level of the calibration mark on the flask after the solid has dissolved,
rather than before?
When a substance is dissolved, there is often a slight change in volume due to the attractions between the solute and solvent particles. Since molar concentration is
measured in mole of solute per litre of solution, it is necessary to accurately measure the volume of solution rather than the volume of water used.
Experimental steps required to prepare a standard solution (e.g. 0.05M Na2CO3 2L)?
1) Calculate the required amount of Na2CO3 in grams.
2) Transfer the solid into a 2L volumetric flask , using a funnel.
3) Wash the watch glass and the funnel so that all the solute dissolves.
4) Half fill the volumetric flask and shake to dissolve the sample fully.
5) Fill up to the calibration line with distilled water until a meniscus if formed.
Difference between standard solution and primary standard?
A standard solution is a solution of accurately known concentration.
A primary standard is a substance that is readily obtained in a pure form, has a known formula and can be stored without deteriorating or reacting with the atmosphere. It should also be cheap and have a high molar mass.
Difference between equivalence point and end point?
The equivalence point in a titration occurs when the reactants have been mixed in the mole ratio shown by the reaction equation.The end point occurs when the indicator changes colour.
Difference between burette and pipette?
A burette is a piece of equipment capable of delivering variable volumes of a liquid accurately (generally up to 50.00 mL), while pipettes usually deliver only a fixed volume of liquid (e.g. 20.00 mL).
Difference between aliquot and titre?
An aliquot is the volume of liquid delivered from a pipette, while a titre is delivered by a burette and is the volume needed to reach the end point of a titration.
