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Flashcards in module 4 Deck (44):

what is an indicator?

is a dye that changes colour depending on whether it's above or below a certain pH.


How do some indicators work?

Contain mixture of dyes, that means thy gradually change colour over a broad range of pH. Called wide range indicators and they're useful for estimating the pH of a solution. E.g. universal indicator gives the colours.


What is a pH probe and how does it work?

Attached to pH meter can also be used to measure pH electronically. Probe is placed in solution you are measuring and pH is given on digital display as numerical value, meaning it's more accurate than indicator.


What is an acid?

Substance that forms aqueous solutions with a pH of less than 7 Acids form H+ ions in water.


What is a base? And what is an alkali?

A base is a substance with a pH greater than 7. An alkali is a base that dissolves in water to form a solution with a pH greater than 7. Alkalis form OH- (revision guide) ions in water.


What is the neutralisation equation?

acid+base=salt+water. Or H+(aq)+OH-(aq)=H2O(l) (revision guide).


What happens when an acid neutralises the base or vice versa?

Products are neutral i.e. they have a pH of 7. An indicator can be used to show that a neutralisation reaction is over.


What can a neutralisation reaction of strong acids and alkalis be useful?

Can be used to calculate the concentration of an acid or alkali by titration.


What are titrations?

Allow you to find out exactly how much acid is needed to neutralise a quantity of alkali-or vice versa.


What do you do to find the concentration of an alkali?

Use a pipette and pipette filler, add a set volume of alkali to a conical flask. Add 2 or 3 drops of indicator too.


What do you use a funnel to do?

To fill burette with some acid of known concentration. Make sure do this bellow eye level-don't want to be looking up if some acid spills over. (wear safety glaces). Record initial volume of acid in burette.


What do you use to burette to do?

Add acid to alkali to bit at time-giving conical flask a regular swirl. Go especially slowly when think end-point (colour change) is about to be reached.


What is the final step of titration when the indicator changes colour and is neutralised?

Record final volume of acid in burette, and use it, along with initial reading to calculate volume of acid used to neutralise alkali.


What do you do to increase accuracy of titration and to spot any anomalous readings?

need several consistent readings.


What does the first titration need to be?

Rough titration to get approximate idea of where solution changes colour (end-point).


Why do you need to repeat the experiment?

To make sure get (pretty much) same answer each time (within 0.10cm3). Calculate mean of results ignoring any anomalous results.


What is universal indicator used for?

To estimate pH of solution because can turn variety of colours. Each colour indicates narrow range of pH values.


What is universal indicator made from and why is it used in titration?

made from mixture of different indicators. Colour gradually changes from red in acidic solutions to violet of alkaline solutions. During titrations between alkali and acid, want to see sudden colour change at end-point.


What are different types of indicator?

Litmus blue-alkalis, red-acid, phenolphthalein pink-alkalis and colourless in acids. Methyl orange. Yellow in alkalis and red in acids.


What happened when they are added to aquous solutions?

They ionise. Produce hydorogen ions. HCL=H+ +CL-


What happens when strong acids are added to water?

Ionise completly. Acid particles dissociate to release H+ ions.


What happens when weak acids are added to water?

Don't fully ionise. Small proportion of acid particles dissociate to release H+ions.


How is ionistation of weak acids a reversible reaction?

sets up equilibrium between undissociated and dissociated acid. Only few of acid particles release H+ ions, position of equilibrium lies well to left. Reactions of acids involve H+ ions reacting with other substances. If H+ concentration higher, rate of reaction will be faster, strong acids will be more reactive than weak acids of same concentration.


Ho does pH measure concentration of hydrogen ions?

Every deacrease in pH, concentration of H+ ions increases by 10. Acid with pH of 4 has 10 times concentration of H+ ions than 5 pH. Decrease of 2 pH. Increases H+ concentration by 100. pH of strong acid less than pH of weaker acid in same concentration.


How is acid strength different to concentrations of acids?

Acid strength tells you the proportion of acid molecules in water. Concentration of acid is different. Concentration measuress how much acid is in a volume of water. Larger amount of acid in certain volume of liquid , more concentrated acid is. Can have dilute but strong acid, or concentrated but weak acid. pH decrease acid concentration increases regardless if strong or weak acid.


What are metal oxides and metal hydroxides?

Some can dissolve in water. Soulble compounds are alkalis. Bases that won't dissolve in water still take part in neutralisation reactons of acids. React with acids to make salt and water.


What are metal carbonates?

Also bases. React with acids to produce salt, water and carbon dioxide.


How do you make soluble salts using an insoluble base?

Need to pick right acid and insoluble base e.g. if want to make copper chloride, could mix hydrochloric acid and copper oxide.


What is the process of making soluble salts using an insoluble base?

Gently warm dilute acid using bunsen burner, then turn off bunsen burner. Add insoulbe base to acid, a bit at a time. When excess solid will just sink to bottom of flask acid is neutralised. Filter out excess sold to get salt solution.


How do you get pure solid crystals of salt?

Gently heat solution using water bath or electric heater to evaporate some water, stop heating and leave to cool. Crystals of salt should form, can be filtered out of solution then dried-crystalisation.


What is the reactivity series purpose?

How easily they can lose electrons to form positive ions and higher reactivity when react with water or acid.


What does metal reacting with acids tell you?

Some metals react with acids to produce salt and hydrogen. Speed of reaction indictated by rate of hydrogen bubbles given off. More reactive, faster bubbles. Also temperature change of reaction with acid or water over set time. If same mass and surface area of metal, more reactive, greater temperature change. Acid+metal=salt+hydrogen.


What is the formula for a raection between a metal and water?

metal+water=metal hydroxide+hydrogen.


What area oxides?

Metals reacting with oxeygen to create an oxide.


How are metals extracted by reduction by using carbon?

the ore is reduced as oxygen is removed, carbon gains oxygen so is oxidised. The position on the reactivity series determins whether can be extracted by reduction with carbon.


What is a redox reaction?

Oxidation can mean addition of oxygen, reduction removal of oxygen. Loss of electrons is oxidation. Gain is reduction. Reduction and oxidation happen sililtaniously.


What is a displament reaction?

if put reactive metal in solution of dissolved metal compound, reactive metal will reaplace less reactive metal. always metal ion gains electrons and is reduced. Metal atom loses electrons and is oxidised.


What is an ionic equations?

Only particles that react and productsw form shown. For a displacment reaction just concentrates on substaqnce which are oxidised or reduced.


What happens during an electrolysis experiment?

Electric current passed through electrode. Ions move towards electrodes, where reaction decomposes. Positive ions will move towards the cathode and gain electrons. Negetive ions will move towards the anode and lose electrons. Creates flow of charge. After lose or gain electrons become discharged from electrolysis.


How does electrolysis work in molten ionic solids?

ionic solids can't be electrolysed because can't move. Molten ionic compounds can be electrolysed, can move freely can conduct electricity. Broken into their elements. Positive metals are reduced at cathode. Negetive non-metals oxidised at anode.


How are metals extracted from their ores?

If too reactive to be reduced with carbon, can't use electrolysis can't be used-too expensive. Aluminium extracted from ore bauxite by electrolysis. Bauxite has aluminium oxide- has high melting point, mixed with cryolite to lower melting point. Molten mixture has free ions,conduct electricity. Aluminium oxide attracted to negetive electrode-pick 3 electrons to become neutral, sink to bottom of tank. Oxygen oins attracted to positive electrode lose 2 electrons. Neutral oxygen combine to make oxygen molecule.


How do you dishcharge ions from water than the solute?

In aqueous solutions as well as ions from ionic compound will be hydrogen/hydroxide ions from water. At cathode if H+ ions and metal ions present hydrogen will be produced if metal ions from elemental metal is more reactive tha nhydrogen. If metal ions from elemental metal will be produced instead. At anode, if OH and halide ions are present, molecules of chloride, bromine or iodine be formed. If not present then OH- ions are dishcharged and oxygen formed.


What happens in electrolysis with chlorine, hydrogen and oxygen as aqueous?

Chlorine bleaches damp litmus paper, turning it white. Hydrogen makes squeaky pop with lighted splint. Oxygen will relight a glowing splint.


What are half equations?

Show reactions at electrode. When combining half equations ,is number of electrons needs to be same for half equation.