Mistake Questions Unit 1 R#1 Flashcards
(13 cards)
Give an advantage of mixing solutions containing equal amounts, in moles, of silver nitrate and sodium chloride.
To make sure that all of the silver nitrate and sodium are fully reacted
Explain why hot water evaporates more quickly than cold water.
Because the particles of hot water have more kinetic energy and can more easily overcome attractive forces, escape and become a gas.
Why can’t the baseline be drawn in ink, and why can’t the level of solvent exceed the height of the baseline.
When the baseline is drawn in ink, it will be dissolved by the solvent and interfere with the chromatogram
When the level of water exceeds the height of the baseline, it will dissolve the inks and ruin the chromatogram
Explain why the molar enthalpy change of the reaction between the ester and water is 0 kJ/mol. In your answer refer to bonds broken and formed.
Because the same bonds are broken and formed, and because the energy taken in to break those bonds is equal to the energy released during the formation of those bonds.
Discuss the environmental problems caused by burying polymers in landfill sites and burning them as ways to dispose of them.
Burying them in landfills takes up space and ruins the landscape. Also, as polymers are inert and non-biodegradable, they don’t decompose naturally, and they will remain in these landfills for a very long time. Burning them releases toxic gases like carbon monoxide that can harm humans, and can also produce greenhouse gases that would lead to global warming
Explain how a student could obtain a chromatogram similar to the one shown in the diagram. (no diagram needed).
Draw the start line in pencil. Use the same food colorings/inks/dyes and the same type of chromatography paper. Place inks (etc.) on the start line. Place the paper into the beaker with the start line above the solvent. Remove paper when spots stop moving. Mark the solvent front. Remove the paper and allow it to dry.
Explain why cracking is useful in the oil industry.
Fractional distillation produces more long-chain hydrocarbons than can be used. So cracking produces shorter-chain alkanes, which are in higher demand. These shorter-chain alkanes are more flammable and can be used as fuels. Cracking also produces alkenes that can be used to make polymers.
A student does a titration to find the accurate volume of sodiumhydroxide solution needed for completeneutralisation. The student starts by using a pipette to transfer 25.0 cm3 of the reaction mixture to a conicalflask. Describe how the student should complete the titration.
Rinse the burette with water to remove any impurites. Rinse the burette with sodium hydroxide, then fill the burette with sodium hydroxide. Add a few drops of indicator to the conical flask. Add sodium hydroxide from the burette until the indicator changes colour permanently. Add sodium hydroxide dropwise near the endpoint. Record initial and final volumes on the burette. Repeat until concordant results.
The student wants to find out the volume of sulfuric acid needed to neutralise 25.0 cm3 of the potassium hydroxide solution. Describe how the student should do this titration.
Assume that all pieces of apparatus are clean and dry.
Use a pipette to add 25 cm3 of potassium hydroxide to the conical flask. Add a few drops of methyl orange to the flask. Add sulfuric acid to the burette and record initial reading. Add sulfuric acid from the burette to the flask, swirling continuously, until the methyl orange indicator turns orange. Take the final burette reading and find the volume of acid added by finding the difference between initial and final burette readings. Repeat the titration while adding the acid dropwise near the end and until concordant results are obtained.
Describe a method a student should use to find out which solids act as catalysts in the decomposition of hydrogen peroxide.
Do experiment without any of the solids. Use a known volume of hydrogen peroxide solution. Measure the time for a certain volume of oxygen gas to be collected. Repeat using the same volume of hydrogen peroxide solution with a known mass of solid X, then for solid Y and Z. Measure the time for the same volume of oxygen to be collected. After the reaction, by filtration, find the mass of each solid. If a solid is a catalyst, then it would reduce the time taken for the oxygen to be collected while still having the same initial mass at the end of the experiment.
Areoplanes are made of an alloy containing aluminium and titanium. Explain why the alloy is stronger than pure titanium metal.
Pure titanium is made of layers of metal ions that can slide over each other. While in an alloy of titanium and aluminium, the different-sized particles distort the regular arrangement of the titanium layers, making it harder for the layers to slide over each other, and thus making the alloy harder.
Describe the industrial process used to separate crude oil into fractions.
Fractional distillation separates the fractions based on their boiling points. Crude oil is vaporised into a mixture of gases. This mixture rises up through a fractionating column where the temperature at the top is cooler than the temperature at the bottom, creating a temperature gradient. This causes the fractions with the lower boiling points to collect at the top and the fractions with the higher boiling points to collect near the bottom. (If asked about a particular fraction, state its general position and what fractions are beneath and above it.)
Explain why straight chain alkenes always have the same empirical formula, but straight chain alkanes have different empirical formulea. Refer to the molecular formulea of alkanes C2H6 and C4H10 in your answer.
The general formula of alkenes is CnH2n so the emprical formula is always CH2. The general formula of alkanes is CnH2n+2, so we can’t divide by n. The empirical formula of C2H6 is CH3 and the empirical formula of C4H10 IS C2H5, so they are different.
