Chem equation

when potassium nitrate and sodium hydroxide react ,

there is no observable change. it is because there are four kinds of ions

in the solution . there are potassium ion , nitrate ion , sodium ion and

hydroxide.(hydrogen ion is relatively very little, so we do not count it)

your miss's both statements are correct. no precipitate and no

colour change.

you should try your best to momerize some facts.

such as all hydroxides are insoluble except potassium , sodium and

ammonium. all nitrates are soluble ....etc.

then you can predict there is a reaction or not.

ok?

樓上, 你既concept有問題wor...

係咪2個都係solution?
冇野出同冇reaction都岩,

首先, double displacement 係2種 aqueous ionic compounds ge reaction,
包括左 precipitation, neutralization 同 gas forming reactions.

由於potassium nitrate 唔係acid, 所以一定冇 neutralization.

因為potassium nitrate 同 Sodium hydroxide 會溶係水,
令到solution 會有K+, NO3-, Na+ 同 OH- 平均分佈,
只要其中一個組合會出到insoluble salt, 就會有precipitation,
但係cation中, K+ 同 Na+ 所form ge 都係soluble salt,
所以冇precipitation.

至於gas forming reactions,
要其中一個組合會係H2CO3或H2SO3先會有,
H2CO3(aq) → H2O (l) + CO2(g)
H2SO3(aq) → H2O (l) + SO2(g)

如果將問題改為iron(ll) nitrate + Sodium hydroxide
咁就會有precipitation, 因為insolube iron(ll) hydroxide is formed

係冇野出，但有Reaction，雙者互相displace，因為兩樣野都係soluble in water，互相交換。而displace之後，KOH同NANO3都係soluble in water，而K+，Na+，NO3+，OH-，都係無色。無顏色變化，無ppt.，又冇gas出，所以，係No observable change。
由以上可知，係No observable change，但有reaction!