Identification of ions and gases
11 flashcards to master Identification of ions and gases
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What is paper chromatography used for?
Paper chromatography is used to separate mixtures of soluble colored or colorless substances using a suitable solvent. It relies on the different solubilities and affinities of the substances for the stationary (paper) and mobile (solvent) phases.
How can paper chromatography identify unknown substances?
Unknown substances can be identified by comparing their chromatograms to those of known substances run under identical conditions. Substances with matching Rf values are likely the same.
How can paper chromatography indicate the purity of a substance?
A pure substance will produce a single spot on the chromatogram. An impure substance will produce multiple spots, indicating the presence of different components.
What is a locating agent, and when is it used?
A locating agent is a substance used to make colorless substances visible on a chromatogram. It reacts with the colorless substances to produce colored spots. Ninhydrin is a common locating agent for amino acids.
State the equation for calculating the Rf value.
Rf = (distance travelled by substance) / (distance travelled by solvent). The Rf value is a characteristic constant for a given substance under specific chromatographic conditions.
A spot travels 3.0 cm on a chromatogram, and the solvent front travels 5.0 cm. Calculate the Rf value.
Rf = (distance travelled by substance) / (distance travelled by solvent) = 3.0 cm / 5.0 cm = 0.6. Remember to include units for working, but the Rf value itself is dimensionless.
Why is it important to use the same conditions when comparing chromatograms?
Rf values are affected by factors such as the solvent used, the temperature, and the type of paper. To accurately compare, all variables except the unknown substance must be constant.
What do the state symbols (s), (aq), (l), and (g) represent?
(s) represents solid, (aq) represents aqueous (dissolved in water), (l) represents liquid, and (g) represents gas. All state symbols must be correct in chemical equations.
In a reaction, 25.0 cm³ of 0.400 mol/dm³ HCl reacts completely. How many moles of HCl are used?
Moles of HCl = (Volume in dm³/1000) x Concentration = (25.0/1000) x 0.400 = 0.0100 mol.
If 0.0100 mol of HCl reacts according to the equation 2HCl + CaCO₃ → CaCl₂ + H₂O + CO₂, how many moles of CO₂ are produced?
From the balanced equation, 2 moles of HCl produce 1 mole of CO₂. So, moles of CO₂ = 0.0100 mol HCl / 2 = 0.00500 mol.
If 0.00500 mol of CO₂ gas is produced, what volume does it occupy at room temperature and pressure (RTP), assuming 1 mole of gas occupies 24000 cm³?
Volume of CO₂ = Moles of CO₂ x Molar volume at RTP = 0.00500 mol x 24000 cm³/mol = 120 cm³.
Key Questions: Identification of ions and gases
What is paper chromatography used for?
Paper chromatography is used to separate mixtures of soluble colored or colorless substances using a suitable solvent. It relies on the different solubilities and affinities of the substances for the stationary (paper) and mobile (solvent) phases.
What is a locating agent, and when is it used?
A locating agent is a substance used to make colorless substances visible on a chromatogram. It reacts with the colorless substances to produce colored spots. Ninhydrin is a common locating agent for amino acids.
What do the state symbols (s), (aq), (l), and (g) represent?
(s) represents solid, (aq) represents aqueous (dissolved in water), (l) represents liquid, and (g) represents gas. All state symbols must be correct in chemical equations.
About Identification of ions and gases (12.3)
These 11 flashcards cover everything you need to know about Identification of ions and gases for your Cambridge IGCSE Chemistry (0620) exam. Each card is designed based on the official syllabus requirements.
What You'll Learn
- 3 Definitions - Key terms and their precise meanings that examiners expect
- 1 Key Concepts - Core ideas and principles from the 0620 syllabus
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