C5: Chemical Changes Flashcards
(15 cards)
What is the method for making copper sulfate salts?
- Using a measuring cylinder, measure 20 cm3 of acid into the beaker.
- Stand the beaker on a tripod and gauze and warm gently until it is almost boiling. Turn off the Bunsen burner.
- Add half a spatula of copper(II) oxide power into the acid and stir using the glass rod.
- Continue adding the copper(II) oxide until no more dissolves. When the copper(II) oxide disappears the solution is clear blue.
- Allow the apparatus to cool completely and then filter the mixture and discard the residue.
- Pour the filtrate into an evaporating basin. Evaporate this gently using a water bath (250cm3 beaker with boiling water) on the tripod and gauze (see diagram). Stop heating once crystals start to form
- Remove the evaporating basin from the heat and leave to crystallise
What is the word equation for the reaction between copper (II) oxide and sulfurice acid?
Copper (II) oxide + Sulphuric acid > Copper Sulfate + Water
What is the method for measuring the pH curve?
- Fill a burette with 0.1 mol/dm3 hydrochloric acid to the 0 cm3 mark. Using a burette clamp, support the burette over a 250 cm3 conical flask
- Use a measuring cylinder to measure 20 cm3 of 0.1 mol/dm3 sodium hydroxide solution and place this in the conical flask.
- Use the pH probe to measure the pH to one decimal place.
- Add 1 cm3 of hydrochloric acid from the burette to the conical flask. Swirl the mixture and record the pH.
- Repeat, adding 1 cm3 portions of hydrochloric acid and recording the pH each time, until a total of 25 cm3 of acid has been added.
- Plot a graph of pH (y axis) against volume of acid added (x axis). Draw a curve of best fit.
What is meant by the pH scale?
The pH scale measures how acidic or alkaline am object is
How can the pH of a solution be measured
By using a pH probe or universal indicator
Explain why the pH increases before the neutral point as alkali is added
The pH increases as H+ ions in the acid react with OH- ions in the alkali, so concentration of H+ ions reduces
What do acids produce in aqueous solutions?
H+ ions
What do alkalines produce in aqueous solutions?
OH- ions
Why is hydrochloric acid classed as a strong acid?
When using universal indicator, the colour changed to red, showing a low pH and thus suggesting a strong acid. Furthermore, it fully dissociates/ ionises when in water
Why is ethanoic acid classed as a weak acid?
Ethanoic acid is classed as a weak acid as it only partially dissociates/ ionises in water. Furthermore, in universal indicator, it turned orange, showing a weaker acid.
Why does hydrochloric acid react faster with magnesium and sodium carbonate than ethanoic acid does?
Hydrochloric acid reacts faster with magnesium and sodium carbonate than ethanoic acid does because hydrochloric is a stronger acid. This results in a full dissociation of ions, meaning more hydrogen ions can bond with magnesium ions, allow the formation of Magnesium chloride or sodium chloride at a faster rate. However in a weaker acid, ions partially dissociate. Subsequently, there are less hydrogen ions due to a lower rate of dissociation, less can form a bond with magnesium or sodium, resulting in a slower reaction.
Hat is the difference between a dilute acid and a concentrated acid?
A dilute acid has the acid molecules dissolved in a large amount of water, so that there is only a low concentration of H ions. Concentrated acids have little to no water molecules mixed with the acid molecules, meaning the concentration of H ions is high.
What is the difference between a strong acid and a weak acid?
A strong acid is an acid that completely ionises/ dissociates in water, having a lower pH, however a weak acid is an acid that only partially ionises/ dissociates in water, having a slightly higher pH
What is the method of how the pH of a strong acid changes as it is diluted by a factor of 10?
- Label 6 test tubes with numbers from 1 to 6 and place them in order in a test tube rack.
- Use a measuring cylinder to put 10 cm3 of 0.1 mol/dm3 hydrochloric acid into the first test tube.
- Transfer 1 cm3 of the solution from test tube 1 into the measuring cylinder and add distilled water up to the 10 cm3 mark. Pour this into test tube 2.
- Transfer 1 cm3 of the solution from test tube 2 into the measuring cylinder and add deionised water up to the 10 cm3 mark. Pour this into test tube 3.
- Repeat this for the rest of the test tubes
- Use the pH probe to measure the pH of each solution, remembering to rinse the probe with distilled water between each reading. Record the pH in the table.
- Calculate the concentration of each solution (C=Original/10^n-1)n= test tube number
How many times is hydrogen concentration multiplied by as pH decreases by 1?
X10
