chap5&6 + QA

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Testing for gases

NH3 - ammonia

colour odour: colourless and pungent smell

test: put moist red litmus paper near the mouth of the test tube

observation: red litmus paper turn blue

CO2 - carbon dioxide

colour odour: colourless and odourless

test: bubble the gas through limewater

observation: white precipitate formed in limewater

MISTAKES:

worksheet 05 atomic structure

mistake: in the periodic table, elements are arranged in order of proton number

period - horizontal

group - vertical

ionic bonding ws 1

electrostatic forces of attraction hold ______ ions and ________ ions together to form _____ + ______

ionic bonds are strong electrostatic forces of attraction between oppositely charged ions ( +ve and -ve )

NOTE:

1. to calculate the relative mass of chlorine

(75% x 35) + (25% x 37) = ?

2. elements of the same group - same valence electrons n chemical properties

elements of the same period - same electron shells

3. nuclide notation

23

11

4. isotopes are atoms of the same elements with same number of protons but different number of neutrons.

- similar chemical properties different physical properties

5. why electrons are attracted to nucleus

electrons are negatively charged and protons are found in the nucleus which are +ve charged

6. why the atom is electrically neutral

there is equal number of positively charged protons and negatively charged electrons

7. 2 valence electrons - dupet

8 valence electrons - octet

8. stable - completely filled valence shell

9. ionic bonding

atoms of metals from +ve ions ( cations) - lose electrons

atoms of non-metals from -ve ions ( anions ) - gain electrons

10. NH4(+) , Ag(+) , Zn(2+) - cations OH(-) , NO3(-) , CO3(2-) , SO4(2-) , PO4(3-) - anions

Testing of anions

CO3(2-) - carbonate

observation: a white precipitate formed in limewater

Cl(-) - chloride

words to look out for - silver nitrate

observation: a white precipitate formed

SO4(2-) - sulfate

words to look out for - barium nitrate

observation: a white precipitate formed

I(-) - iodide

words to look out for - silver nitrate

observation: a pale yellow precipitate formed

NO3(-) - nitrate

words to look out for - aluminium + sodium hydroxide

observation: ammonia evolved, gas turns red litmus paper into blue

Testing of cations

CA(2+) - calcium ion

observation: a white ppt formed (aqOH)

no ppt formed (aqNH3)

PB(2+) - lead(II) ion

observation: a white ppt formed , soluble (aqOH)

a white ppt formed , insoluble (aqNH3)

Zn(2+) - zinc ion

observation: a white ppt formed , soluble (aqOH & aqNH3)

Fe(2+) - iron (II) ion

observation: dirty green ppt formed , insoluble (aqOH & aqNH3)

Cu(2+) - copper (II) ion

observation: light blue ppt formed , insoluble (aqOH)

light blue ppt formed , soluble (aqNH3)

Fe(3+) - iron (III) ion

observation: reddish brown ppt formed , insoluble ( aqOH & aqNH3)

NH4(+) - ammonia ion

observation: ammonia evolved , turn red litmus paper into blue , no ppt formed , colourless and pungent smell ( aqOH)

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