Chemistry Measurement and Separation Techniques

Comprehensive flashcards covering measurement instruments, gas collection and drying, chemical substances, purity analysis, and separation techniques and chromatography.

What is the SI unit and accuracy of the digital stopwatch mentioned in the lecture?

The SI unit is seconds ($s$) with an accuracy of up to $\text{plus minus } 0.01s$.

How is the temperature in Kelvin ($K$) calculated from degrees Celsius ($^{\circ}C$)?

$$K = \,^{\circ}C + 273$$

What is the accuracy of an electronic balance when measuring mass?

The accuracy is up to $\text{plus minus } 0.01g$.

What is the difference between a pipette and a burette regarding the volume of liquid they measure?

A pipette is used to measure fixed volumes of liquids (e.g., $20.0\,cm^3$), whereas a burette is used to measure variable volumes of liquids (e.g., up to $50.00\,cm^3$).

What is the accuracy of a burette reading?

A burette measures to the nearest $0.05\,cm^3$ and readings are recorded to 2 decimal places.

What two physical properties determine the method used for collecting gases?

1. Solubility in water and 2. Density as compared to air.

Which gases are suitable for collection by the displacement of water method?

Gases that are insoluble or slightly soluble in water, such as Hydrogen, Carbon Dioxide, and Oxygen.

What are the criteria for using the downward delivery method to collect a gas?

The gas must be soluble in water and denser than air.

What is the approximate relative molecular mass ($M_r$) of air used as a reference for gas density?

The $M_r$ of air is around $28.8$.

Which method is used to collect Ammonia, and why?

Upward delivery, because Ammonia is soluble in water and less dense than air.

Why is concentrated sulfuric acid unsuitable for drying alkaline gases like ammonia?

Because a neutralization reaction occurs ($\text{Acid} + \text{Alkali} = \text{neutralisation}$).

Which drying agent is appropriate for drying alkaline gases?

Calcium Oxide ($CaO$).

Define a compound based on the lecture notes.

A compound is a pure substance formed when 2 or more elements are chemically combined.

How do mixtures differ from compounds in terms of melting and boiling points?

Compounds have fixed melting and boiling points, while mixtures melt and boil over a range of temperatures.

What are the four types of molecules mentioned?

Monatomic, Diatomic molecule, Triatomic molecule, and Polyatomic molecule.

How do impurities affect the melting and boiling points of a substance?

Impurities lower the melting point of a solid and increase the boiling point of a liquid.

What is the purpose of chromatography in sports medicine?

To separate and identify substances in blood and urine to determine if athletes have been using banned performance-enhancement drugs.

What is the formula for calculating the $R_f$ value in paper chromatography?

$$R_f = \frac{\text{distance traveled by the component}}{\text{distance travelled by the solvent}}$$

What is a locating agent?

A substance that reacts with colorless substances on chromatography paper to produce a colored product, allowing measurements for $R_f$ values.

How is crystallization different from evaporation to dryness for obtaining a solute?

Crystallization is used for substances that decompose when heated (e.g., sugar or copper (II) sulfate), whereas evaporation to dryness is used for stable solids like salt ($NaCl$).

When is simple distillation used?

To obtain a solvent from a solution, such as obtaining water from sea water.

What is the function of a fractional column in fractional distillation?

To separate different vapors when many liquids with different boiling points are being heated.

What method is used to separate a mixture where one solid sublimes, like iodine and sand?

Sublimation.

What technique is used to separate immiscible liquids like oil and water?

A separating funnel, where the denser liquid sinks to the bottom and is removed via a tap.