Answer:
<u>-16200J</u>
Explanation:
(257J/g)(62.9g)
eliminate the variables
u get 16165.3
go to 3 significant digits
u get 16200
and since it is freezing we are taking out energy so it would be
-16200J
Answer:
4.68x10²⁵ ions of Na⁺
Explanation:
First of all, we dissociate the salt:
NaCl(aq) → Na⁺(aq) + Cl⁻(aq)
An aqueous solution of NaCl dissociates in chlorides anions and sodium cations. Ratio is 1:1, per 1 mol of NaCl, we have 1 mol of Na⁺
We determine the moles of salt: 4543.3 g . 1mol / 58.45 g = 77.7 moles
77.7 moles are the amount of NaCl, therefore we have 77.7 moles of Na⁺.
We count the ions:
1 mol fo Na⁺ has 6.02x10²³ ions
77.7 moles of Na⁺ must have (77.7 . 6.02x10²³) / 1 = 4.68x10²⁵ ions of Na⁺
For the first one the pattern is multiply the previous number by five as you see 1 x 5 = 5 and so on. To keep adding to it you would do
125 x 5 = 625 625 x 5 = 3125 3125 x 5 = 15625
Now for the second one the pattern is divide the previous number by three as you can see 2187 / 3 = 729 and so on. To keep going you would
81 / 3 = 27 27 / 3 = 9 9 / 3 = 3
I hope this helps you and if you have anymore questions i'll be glad to answer them.
Answer:
pKa = 3.675
Explanation:
∴ <em>C</em> X-281 = 0.079 M
∴ pH = 2.40
let X-281 a weak acid ( HA ):
∴ HA ↔ H+ + A-
⇒ Ka = [H+] * [A-] / [HA]
mass balance:
⇒<em> C</em> HA = 0.079 M = [HA] + [A-]
⇒ [HA] = 0.079 - [A-]
charge balance:
⇒ [H+] = [A-] + [OH-]... [OH-] is negligible; it comes from to water
⇒ [H+] = [A-]
∴ pH = - log [H+] = 2.40
⇒ [H+] = 3.981 E-3 M
replacing in Ka:
⇒ Ka = [H+]² / ( 0.079 - [H+] )
⇒ Ka = ( 3.981 E-3 )² / ( 0.079 - 3.981 E-3 )
⇒ Ka = 2.113 E-4
⇒ pKa = - Log ( 2.113 E-4 )
⇒ pKa = 3.675
Avogadro's number is the number of atoms in one mole of a substance. The number is 6.022 x 10^23 atoms/mol. So, if you have 1 mole of carbon atoms, there will be 6.022 x 10^23 atoms in that sample.
Hope this helps
