Chemical Changes Flashcards
what is thermal decomposition?
process in which substance broken down into 2 or more simpler substances by the effect of heat
what is combustion?
combination of a substance with oxygen in presence of heat (releases a lot of energy)
what is electroplating?
process in which a substance is coated with a metal with the passage of an electric current
what is electrolysis?
chemical decomposition of substances with passage of an electric current
what are acids?
substance that produces hydrogen ions (acidic properties) in aqueous solution
what are 4 common acids?
hydrochloric acid (HCl)
nitric acid (HNO₃)
sulfuric acid (H₂SO₄)
phosphoric acid (H₃PO₄)
what is the basicity of an acid?
number of hydrogen ions which can be produced by one molecule of the acid (monobasic, dibasic, tribasic)
what are 2 properties of acids? (taste/texture and pH)
sour taste
pH <7
what are the effects of acids on litmus paper and universal indicator?
turns blue litmus paper red (no effect on red litmus paper)
turns universal indicator from green to yellow/orange/red depending on pH
why do acids only display their properties when added to water?
acids produce hydrogen ions in aqueous solutions, which gives acids their properties
what are salts?
ionic compounds formed when metal/ammonium ions replace 1 or more hydrogen ions of an acid (e.g. KCl)
what is the equation for acids and reactive metals?
acid + metal –> salt + hydrogen
forms salt + hydrogen gas
what are the 2 observations of acid-metal reactions?
effervescence of colourless and odourless gas
grey solid (metal) dissolves to form colourless solution
what is the equation for acids and metal carbonates?
acid + metal carbonate –> salt + water + carbon dioxide
forms salt + water + carbon dioxide
what are the 2 observations of acid-metal carbonate reactions?
effervescence of colourless and odourless gas
white solid (metal carbonate) dissolves to form colourless solution
what are metal carbonates?
ionic compounds containing metal cation and carbonate ion (e.g. CuCO₃)
what is the equation for acids and bases?
acid + base –> salt + water
forms salt + water only
neutralisation
what are bases?
metal oxides/hydroxides that react with acids to form salt and water only
how do you test for hydrogen gas (colourless/odourless)?
place lighted splint at mouth of test tube
what is the observation of the test for hydrogen gas?
hydrogen will extinguish lighted splint with ‘pop’ sound
how do you test for carbon dioxide gas (colourless/odourless)?
bubble gas into limewater (aqueous calcium hydroxide)
what is the observation of the test for carbon dioxide gas?
carbon dioxide will form white precipitate with limewater
how do you test for ammonia gas (colourless/pungent)?
damp red litmus paper
what is the observation of the test for ammonia gas?
ammonia gas will turn the damp red litmus paper blue
what are alkalis?
substance that produces hydroxide ions (alkaline properties) in aqueous solution
bases that are soluble in water
what are 4 alkalis?
sodium hydroxide (NaOH)
calcium hydroxide [Ca(OH)₂]
aqueous ammonia [NH₃(aq)]
potassium hydroxide (KOH)
SCAP hydroxide [ammonia is special :)]
what are 4 insoluble bases?
magnesium oxide (MgO)
lead(II) oxide (PbO)
iron(III) oxide (Fe₂O₃)
zinc oxide (ZnO)
ZILM oxide
what are 2 properties of alkalis? (taste/texture and pH)
bitter taste, soapy feel
pH 7>
what are the effects of alkalis on litmus paper and universal indicator?
turns red litmus paper blue (no effect on blue litmus paper)
turns universal indicator from green to blue/violet depending on pH
why are both acids and alkalis good conductors of electricity in aqueous solutions?
they contain mobile ions
what is the equation for alkalis and acids?
alkali + acid –> salt + water
forms salt + water only
neutralisation
what is neutralisation?
process in which hydrogen ions (H⁺) from acids and hydroxide ions (OH⁻) from alkalis react to form water
what is the ionic equation for neutralisation?
H⁺(aq) + OH⁻(aq) —> H₂O(l)
what is the equation for alkalis heated with ammonium salts?
alkali + ammonium salt -(heat)-> salt + water + ammonia
produces salt + water + ammonia gas
what are ammonium salts?
salts containing ammonium ions (e.g. ammonium nitrate)
what is the concentration of a solution?
the amount of a solute dissolved in a unit volume of solution
what are concentrated and diluted solutions?
concentrated: large number of particles of a substance in a fixed volume of water
diluted: small number of particles of a substance in a fixed volume of water
what is a saturated solution?
solution formed when the maximum amount of solute has been dissolved in a fixed volume of solvent at a fixed temperature
what is the concentration of ions in acids?
higher concentration of hydrogen ions, lower concentration of hydroxide ions
what is the concentration of ions in neutral solutions?
contains equal number of hydrogen and hydroxide ions
what is the concentration of ions in alkalis?
higher concentration of hydroxide ions, lower concentration of hydrogen ions
what are 2 ways to measure pH?
indicators (chemical compounds)
pH meter
what is an indicator?
substance which changes colour depending on whether a solution is acidic/alkaline
what is a pH meter?
digital instrument which gives a numerical pH value by measuring pH electrically
why is a pH meter more accurate and reliable than indicators?
we can only approximate the pH values of substances from the colour of indicators
what are 3 types of indicators?
methyl orange
litmus
phenolphthalein
what are the properties of methyl orange? (colour in acids/alkalis, pH which colour changes)
in acidic solutions: red
pH which colour changes: 3-5
in alkaline solutions: yellow
what are the properties of litmus? (colour in acids/alkalis, pH which colour changes)
in acidic solutions: red
pH which colour changes: 5-8
in alkaline solutions: blue
what are the properties of phenolphthalein? (colour in acids/alkalis, pH which colour changes)
in acidic solutions: colourless
pH which colour changes: 8-10
in alkaline solutions: pink
what are 3 beneficial effects of chemical changes?
decomposition of dead organisms breaks down unwanted matter and releases nutrients back to the earth
cooking food
household detergents for cleaning
medicines, insecticides
jet fuel combustion to produce energy to move planes
what are 3 harmful effects of chemical changes?
air pollution from combustion harmful to health (acid rain, corrodes buildings, destroys aquation life)
iron structures like bridges rust, becomes corroded and unsafe
decomposition leads to wastage of food supplies and resources
what are 3 unreactive metals?
copper
gold
silver
