Question

21. List 3 indicators of a chemical change.

Answer 1

21. change in temperature, change in color, or noticeable odor (after reaction has begun)

22. Picture...  Wasn't so sure about this since no charge was given, so I suspected it has a charge of 2. If you have more information on this I would be glad to help, and I can't tell what is happening with the calculations given. It would be helpful if you can add spaces or put a line break.

23. An ion is an atom or molecule with an electric charge. It is formed when atoms lose or gain electrons. There are two types of ions: cations (net positive charge) and anion (net negative charge).

24. Picture

25. a) dinitrogen tetrahydride

     b) phosphorus triiodide

     c) lithium hydroxide

Answer 2

Answer:

See explanation.

Explanation:

Hello,

21. In this case the three main indicators of a chemical change is a temperature change, a color change and/or the release of bubbles. All of them are indicators of a change in the composition of the initial reactants.

22. In this case, the correct conversion is:

$n_{Zn(OH)_2}=0.45gZn(OH)_2*\frac{1molZn(OH)_2}{99.424gZn(OH)_2}=4.5x10^{-3}molZn(OH)_2$

In such a way three errors are: it starts by 0.45 g not 0.65 g, zinc hydroxide's molar mass is 99.424 g/mol as its formula is Zn(OH)₂ not 82.41 g/mol and the given Avogadro's number turns needless.

23. An ion is defined as a charged species coming from the ionization of an atom or a molecule, it means, when they either lose or gain electrons depending on the case. There exist two types of ions: cations (net positive charge) and anion (net negative charge).

24.

a. $Br^{-1}$ as it has seven valance electrons, it needs one electron to attain the octet.

b. $H^{+1}$ as it loses one electron when forming a cation.

c. $Se^{-2}$ as it has six valance electrons, it needs two electrons to attain the octet.

25.

a. Hydrazine: covalent, base.

b. Phosphorus triiodide: covalent, base.

c. Lithium hydroxide: ionic, base.

Best regards.