CHEM 120L: Reactions of Copper

reactions of copper: filtrate

substance passing through a filter; liquid in the glass of the Buchner funnel

reactions of copper: decant

carefully pour off liquid from a mixture; copper solid at the end is decanted from the Zn HCl mixture

reactions of copper: supernatant

liquid sitting on top of a solid or heavier liquid; solution above black CuO and solution above copper solid at the end

reactions of copper: gelatinous

jelly-like and thick; used to describe the Cu(OH)2 solution before heating and decomposing into CuO

reactions of copper: coagulate

to clump together or thicken; mixing of the CuO with heating is done to achieve this

reactions of copper: bumping

violent boiling and bubbling of a liquid; stirring the Cu(OH)2 while heating is done to prevent this

reaction 1: copper metal to copper (II) nitrate

nitric acid is added to almost completely pure copper wire → water, brown NO2 gas and blue copper 2 nitrate produced

what is excess in the reaction of copper and nitric acid

nitric acid; doesn’t need to be an exact measurement

reaction 2: copper (II) nitrate to copper (II) hydroxide

add DI water to the cupper nitrate/acid solution (one exception of acid to water rule), add NaOH to Cu(NO3)2 → gelatinous Cu(OH)2 and check the pH >10

reaction 3: copper (II) hydroxide to copper (II) oxide

copper (II) hydroxide decomposes into copper oxide and water by heating with Bunsen burner

filtration step of CuO

small portions of DI are used to quantitatively transfer all CuO from the beaker to the buchner funnel. each rinse is swirled and used to rinse the solid on the filter paper to remove NaNO3 and NaOH

reaction 4: copper (II) oxide to copper (II) sulphate

• dilute H2SO4 is used to rinse the filter paper containing CuO back into the container it was heated from

• dropper used to draw acid up and continue rinse of funnel

• DI used to rinse acid

• solution swirled to dissolve CuO

what should you do if the CuO isnt dissolving in the H2SO4

check with TA, more acid might be needed or slight heating

rxn 5: copper (II) sulphate to metallic copper

• single displacement by Zn solid occurs to obtain finely divided solid copper. H2 gas fizzing occurs in side rxn, thus snorkel exhaust vent is used

• swirl until blue color disappears

what side reaction occurs to produce H2 gas when Zn is added to the Cu (II) sulphate

Zinc reacts with acid to form H2 gas

rxn 6: removing excess zinc

• add HCl to copper, zinc aqueous solution

• swirl to speed reaction, H2 gas produced

• all zinc is gone when H2 bubbles stop, no silver

isolating drying and weighing the copper

• settle the copper, decant the supernatant

• wash twice with DI, decant into a clean beaker

• transfer to evaporating dish with as much DI needed, decant, heat with a cool flame

• when a little water left stop heating and cool until comfortably warm

• weigh

common mistakes

• wrong container

• not stirring Cu(OH)2 while heating

• adding the wrong acid to CuO

• loss of product during filtration

• loss of product during decanting

what happen when copper is reacted with HNO3 in a erlenmeyer instead of beaker

it’ll take much longer as gas can’t escape as freely

what happens when Cu (II) OH not stirred while heating

vigorous bumping

what happen if wrong acid is added to CuO

• HCl → bright green, wrong

• HNO3 → bubbling and fuming like rxn 1, wrong

• H2SO4 → bright blue, correct!

what causes product to be lost when filtering

• small filter paper, creased/folded/teared paper, dry paper can cause CuO to be drawn into filtrate

• needs to be filtered again

what to do when product lost while decanting

if the product isn’t contaminated, you can decant the liquid again and recover the solid