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allsm [11]
3 years ago
10

When was helium discoved?

Chemistry
1 answer:
andrey2020 [161]3 years ago
4 0
It was discovered in 1868.i hope this helps you .
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Calculate the pH in titration of a weak acid: What is the pH in titration of formic acid (HCHO2, 0.200 M, 100.0 mL) after the ad
ki77a [65]

Answer:

pH = 12.61

Explanation:

First of all, we determine, the milimoles of base:

0.120 M = mmoles / 300 mL

mmoles = 300 mL . 0120 M = 36 mmoles

Now, we determine the milimoles of acid:

0.200 M = mmoles / 100 mL

mmoles = 100 mL . 0.200M = 20 mmoles

This is the neutralization:

HCOOH    +     OH⁻         ⇄        HCOO⁻     +    H₂O

20 mmol       36 mmol             20 mmol

                    16 mmol

We have an excess of OH⁻, the ones from the NaOH and the ones that formed the salt NaHCOO, because this salt has this hydrolisis:

NaHCOO  →  Na⁺  +  HCOO⁻

HCOO⁻  +  H₂O  ⇄   HCOOH  +  OH⁻   Kb →  Kw / Ka = 5.55×10⁻¹¹

These contribution of OH⁻ to the solution is insignificant because the Kb is very small

So:  [OH⁻] =  16 mmol / 400 mL →  0.04 M

- log  [OH⁻]  = pOH →  1.39

pH = 14 - pOH → 12.61

6 0
3 years ago
If the ka of a monoprotic weak acid is 1.2 × 10-6, what is the ph of a 0.40 m solution of this acid?
frez [133]
First, we write out a balanced equation.
HA <--> H(+) + A(-)

Next, we create an ICE table

        HA     <-->      H+     +    A-
[]i     0.40M            0M           0M
Δ[]    -x                   +x            +x
[]f     0.40-x             x              x

Next, we write out the Ka expression.

Ka = [H+][A-]/[HA]

Ka = x*x/(0.40-x) 

However, because Ka is less than 10^-3, we can assume the amount of dissociation is negligible. Thus,

Assume 0.40-x ≈ 0.40

Therefore, 1.2x10^-6 = x^2/0.40

Then we solve for the [H+] concentration, or x

\sqrt{0.40(1.2*10^{-6})} =x

x=6.93x10^-4

Next, to find pH we do 

pH = -log[H+]

pH = -log[6.93x10^-4]

pH = 3.2
5 0
3 years ago
Did diagram shows embryo development of four different animals. How is this evidence used to suggest that life changes over time
wel
It suggests that life changes over time by showing different animals at different stages in their life, also giving more than one example on how they can change during early development and throughout their lives
5 0
4 years ago
Read 2 more answers
Which two electron configurations represent elements that would have similar chemical properties? (1) 1s22s22p4 (2) 1s22s22p5 (3
Anton [14]

Answer: Two electron configurations of elements that would have similar chemical properties are (2) and (4).

Explanation:

(1) 1s^22s^22p^4

(2) 1s^22s^22p^5

(3) [Ar]4s^23d^5

(4) [Ar]4s^23d^{10}^4p^5

Valence electrons : These are the electrons present in last principal quantum number of an atom of the element.

Two electron configurations represent elements that would have similar chemical properties are (2) and (4). This is because number of valence electrons present in both of them are same that is seven valence electrons . Also valence electrons of both the elements are present in p-orbital which means that they both belongs to same group  in a periodic table. The members of same group in a periodic table have similar chemical properties.

3 0
3 years ago
What is the noble gas electron configuration of bismuth (Bi)? A. [Kr] 6s2 6p3 B. [Xe] 6s2 6p3 C. [Xe] 4f14 5d10 6s2 6p3 D. [Kr]
OlgaM077 [116]

The answer is C) Xe 4f14 5d10 6s2 6p3

4 0
4 years ago
Read 2 more answers
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