Analysing water for salts Flashcards
Why is pure water a poor electrical conductor?
Pure water has no mobile charged particles. However due to water’s self ionisation it does have some charged particles but the amount of these is so small, little to no electricity can be conducted.
Why can non pure water conduct electricity?
Due to the presence of dissolved ions and other contaminants, water is able to conduct electricity. eg cl-, k+
What is one way to measure the amount of ions in a solution?
Testing its electrical conductivity will show roughly, how many ions are in the solution. The more ions, the higher the electrical conductivity.
What is qualitative and quantitative analysis?
Use of experimental procedures to determine..
Qualitative: WHICH elements are in a substance.
Quantitative: how much of an element
What is colorimetry?
Involves shining light of complementary colour through the solution and measuring the amount absorbed. The amount of light that passes through the solution reflects how concentrated the solution is.
What is UV–visible spectroscopy?
Measures the absorption of light at a particular frequency. Can be used both qualitatively and quantitatively.
What is the difference between colorimetry and UV–visible spectroscopy?
- colorimetry uses a light that is complementary to the compound
- UV-S measures the absorption of light at a particular frequency
What type of element is the UV-spectroscopy used for and why?
Organic substances, ie. non metals
UV light gives off a high amount of energy, This enables the non metals that have more valence electrons to absorb this energy.
What is the AAS?
This is a spectroscopy process that uses a hollow cathode lamp, made out of the metal being tested. In this way only the light emitted from that lamp can be absorbed by that same element.
How does a spectroscopy technique determine the concentration of a substance?
By emitting light through a prism or a filter, the light will pass through the solution. Depending on how concentrated the solution is, the light will be slightly or fully absorbed. This is because valence electrons absorb the energy and are promoted to higher energy levels.
What is gravimetric analysis?
Lab techniques used to determine the mass or concentration of a substance by measuring a change in mass.
What is stoichiometry?
The study of the amount and ratio of reactants and products in a chemical reaction.
Why is a mixture sometimes heated before being gravimetrically analysed?
The heating or chemical decomposition separates out any volatile compounds, which results in a change in mass that we can measure.
How can you determine that mass of MgCl2 and NaNO3 is a mysterious solution?
Add an excess of the precipitating agent, AgNO3. It will from the precipitate with Cl. Measure the precipitate, write the equation and calculate the amount of mole of AgNO3 that was used. Then use the mole ratio to calculate the rest.
What does a chemical reaction not tell us?
A chemical equation does not indicate the rate (how fast) or extent (how far) of a reaction.
