Why is Na2CO3 added slowly, with stirring, to the beaker?
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| Term | Definition |
|---|---|
Why is Na2CO3 added slowly, with stirring, to the beaker? | To prevent the formation of hard lumps of sodium carbonate that are hard to dissolve. |
What is the concentration of a solution determined by? | It's determined by reacting that solution with another solution of a known concentration (primary standard or secondary standard). |
What is the end point / equivalence point? | The point at which the two solutions have reacted completely. |
The concentration of a solution is recorded by... | The volumes of the two solutions at end point. |
Role of a graduated cylinder? | Measured volume, isn't accurate due to wide neck. |
Role of volumetric flask? | Contains a definite amount of a solution. Calibration mark to ensure solution is accurate. Mix via inverting (homogenous mixture). Base of meniscus rests on mark. |
Role of pipette? | Designed to draw up a precise amount of solution, usually 25 cm3. |
Role of burette? | Fill above mark and open to ensure bottom is filled with liquid, no air bubbles. Shows volume decreasing downwards. |
Role of conical flask? | Shape suitable for swirling. Place white tile underneath to see colour change clearly. |
Role of pestle + mortar? | Used to break down any solid into smaller pieces so that it can be easily dissolved in a solution. |
What is the indicator used? | To use the standard solution of sodium carbonate to standardise HCl | Methyl orange, yellow to pink. |
Describe using the standard solution of sodium carbonate to standardise HCl. | Pour HCl solution into a beaker, rinse out burette and prepare it, rinse out burette with HCl then fill with HCl above the zero mark. Allow to flow until @ zero, use white tile to see colour change, record liquid, rinse out pipette with DI water and Na2CO3 into clean conical flask, add methyl orange indicator- note colour, carry out a rough titration- note burette reading, pipette Na2CO3 into flask, repeat titrations for more accurate reading - within 1 cm3, stop when definite colour change, calculate the conc of HCl. |
Describe the appearance of sodium carbonate. | White solid. |
Why must the mass of sodium carbonate dissolved in the water be known accurately? | So that the concentration of the Na2CO3 can be calculated accurately. |
Why is Na2CO3 a primary standard? | It can be obtained in a pure and stable form. |
State two benefits of a volumetric flask for making up the solution. | The volume of the solution is accurately known. The design of the solution allows it to be shaken easily to ensure a homogenous solution. |
Why is it not recommended to pipette directly from the volumetric flask? | Risk for glass breakage. |
Why is it important not to add too much indicator? | Indicators are either weak acids or weak bases- too much could affect the accuracy of the result. Too much indicator could give a very intense colour that may make it hard to see the colour change at the end point. |
why do we have to standardise HCl solution | To use the standard solution of sodium carbonate to standardise HCl | HCl is not a primary standard. |
Why carry the experiment out more than once? | More accurate titration figure - average of two readings agreeing within 0.1 cm3 is used. |
Appearance of isolated sodium carbonate? | White crystalline solid. |
name the indicator used and its colour change make a 0.1 M of sodium hydroxide, standardise it with a standard HCl sln+ prepare sodium chloride sample | Methyl orange, yellow to pink. |
to find the end point accuratly make a 0.1 M of sodium hydroxide, standardise it with a standard HCl sln+ prepare sodium chloride sample | Rinse burette, pipette… using pipette, transfer NaOH into conical flask, add indicator. Fill burette with HCl. |
To obtain a sample of salt make a 0.1 M of sodium hydroxide, standardise it with a standard HCl sln+ prepare sodium chloride sample | Add NaOH to beaker, just enough HCl to neutralise it (NO INDICATOR). Gently heat the solution until all the water has evaporated to dryness. Sodium chloride will remain in its beaker. |
another suitable indicator for this reaction? make a 0.1 M of sodium hydroxide, standardise it with a standard HCl sln+ prepare sodium chloride sample | Methyl red/ phenolphthalein. |
why is it undesirable to put sodium hydroxide solution into the beaker rather than the conical flask make a 0.1 M of sodium hydroxide, standardise it with a standard HCl sln+ prepare sodium chloride sample | If the burette is not washed out properly after use, sodium hydroxide may crystallise in the Teflon tap-causing blockage of the burette nozzle or changing the concentration of a diluted solution. |
what indicator is used and what colour does it change | Dertermination of the concentration of thanoic acid in vinegar | Phenolphthalein, pink to colourless. |
Describe how to determine the concentration of ethanoic acid in vinegar. | Dilute vinegar with water to calibration mark of a volumetric flask. Rinse out pipette and burette with their respective solution. Place NaOH into conical flask with a couple drops of phenolphthalein indicator. Fill burette with vinegar. Carry out titration. Calculate concentration of ethanoic acid in diluted vinegar solution. |
Why is the vinegar diluted | Dertermination of the concentration of thanoic acid in vinegar | Avoid a very small titre, which would reduce the accuracy of the experiment. Also reduces the amount of vinegar and NaOH needed. |
what is the Indicator used, describe its colour Dertimination of the amount of water crystallisation in hydrated sodium carbinate | Methyl orange, yellow to pink. |
Method of determining the amount of water crystallisation in hydrated sodium carbonate? | Weigh the hydrated sodium carbonate correctly, dissolve in DI water. Transfer to volumetric flask… titrate the Na2CO3 solution against HCl. Repeat until the readings agree within 0.1 cm3. Calculate the concentration of hydrated sodium carbonate. |
What was done to the volumetric flask and its contents immediately after the solution had been made up to the mark with deionised water? Why was it important to do this? | It was stoppered, and then inverted several times. To ensure a homogeneous solution. |
Describe the physical appearance of hydrated sodium carbonate. | White crystalline solid. However, if larger crystals are purchased, these tend to have a clear glassy appearance. |
Explain water of crystallisation. | Water chemically bound in the compound, which gives rise to the crystalline form or water present in definite proportions in crystalline compounds. |
Name another compound that has water of crystallisation present. | Hydrated copper sulfate. |