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What did the periodic table help scientists discover?

Natalija [7]

Answer:

A_________________________

4 0

3 years ago

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An element with atomic number 18 is a noble gas.Into which family you shall place elements with atomic number 17 and 19 and why?

SVEN [57.7K]

Answer:

Explanation:

An element with atomic number 18 is a noble gas.

The element with atomic number 19 will have one extra electron so it can donate one electron or shed one electron to attain noble gas configuration .

It tends to shed one electron to become positively charged ion . Hence they are electro-positive elements .

Similarly the element with atomic number 17 will have one short electron so it can gain one electron to attain noble gas configuration .

They tend to gain one electron to become negatively charged ion . Hence they are electro-negative elements . They have high electronegativity .

5 0

3 years ago

The following is a list of weak acids and their Ka values.HOCl hypochlorous acid 3.5 x 10^-8H2S hydrogen sulfide 1.1 x 10^-7HCN

notsponge [240]

Answer:

(a) HNO₂ nitrous acid 4.5 x 10^-4 is strong acid

(b) Ka expression $Ka = \frac{[H^{+}][NO_{2} ^{-}] }{[HNO_{2}] }$

(c) List of Conjugate Bases

OCl⁻, S²⁻, CN⁻, NO₂⁻

(d) cyanide ion is strongest conjugate base.

(e) pH and pOH of Hypochlorous acid = 4.22 & 9.77

pH and pOH of hydrogen sulfide = 4 & 10

pH and pOH of hydrocyanic acid = 5.2 & 8.79

pH and pOH of nitrous acid = 2.17 & 11.8

Explanation:

(a) Ka and acidity are directly proportional to each other

hence nitrous acid is the strongest acid since it has highest Ka value.

(b) Ka expression of nitrous acid

HNO₂ → H⁺ + NO₂⁻

⇒ $Ka = \frac{[H^{+}][NO_{2} ^{-}] }{[HNO_{2}] }$

(c) Conjuagte base for HOCl hypochlorous acid = OCl⁻(hypochlorite ion)

H₂S hydrogen sulfide = S²⁻(sulphide ion)

HCN hydrocyanic acid = CN⁻(cyanide ion)

HNO₂ nitrous acid = NO₂⁻(nitrite ion)

<u>(d) We know according to Bronsted acid base concept Weak acid have strongest conjugate base</u>

according to this hydrocyanic acid is weak acid so the corresponding conjugate base i.e. cyanide ion is strongest conjugate base.

5 0

3 years ago

In Earth’s mantle there are convection currents. The convection currents flow in a _________ shape. As the hot magma ___________

muminat

Answer:

4

5

2

6

3

1

6

7

.......

.

..

6 0

3 years ago

C2H5OH(l)+CH3COOH(l) → CH3COOC2H5(l)+H2O(l) If the yield of ethyl ethanoate obtained when 20.00 g of ethanol is reacted with exc

vodomira [7]

Answer:

The percentage yield is 79.12%

Explanation:

The first thing we need to calculate here is the theoretical yield of ethyl ethanoate that can be obtained from 20g of ethanol.

Since the mole ratio is 1:1, then this is quite straightforward.

What we need to obtain at first here is the number of theoretical moles of ethanol reacting.

That would be mass of ethanol/molar mass of ethanol

Molar mass of ethanol is 46g/mol

Thus the number of moles is 20/46 = 0.4348 mole

Like it is indicated earlier, since the number of moles are equal from the balanced equation, it also means that 0.4348 mole of ethylethanoate is produced

Now, we need to know the mass of ethyl ethanoate produced

The mass can be calculated by multiplying the number of moles by the molar mass

The molar mass of ethyl ethanoate is 88g/mol

So the mass of it produced = 0.4348 * 88 = 38.2624 or let’s just say 38.26

Thus, the percentage yield will be;

Actual yield/Theoretical yield * 100%

From the question, our actual yield is 30.27g while our calculated theoretical yield is 38.26g

= 30.27/38.26 * 100% = 79.12%

5 0

3 years ago