Chemistry, 02.12.2019 02:31 leasiamoore

How do you prepare a 250 ml of a 2.35 m hf dilution from a 15.0 m solution

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Answer from: mp515

In dilution problems involving known concentrations and volumes of the solution, a widely used equation is:

C1V1 = C2V2

Where:
C1 = Concentration of Solution 1
V1 = Volume of Solution 1
C2 = Concentration of Solution 2
V2 = Volume of Solution 2

Substituting the given values gives: (2.35 M)*(250mL) = (15.0 M)*V2

V2 = 39.17 mL

So, you must initially have 39.17 mL of 15 M solution and dilute it to 250 mL to achieve a 2.35 M solution

Answer from: Quest

it's c. elements are placed in rows based on how may valencies electrons have.

Answer from: Quest

assuming that your periodic table has eighteen columns, you should highlight the four elements in the third column from the left of the table.

explanation

neutral atoms of elements after calcium contain d electrons. the energy of d orbitals of a particular main shell lies between the energy of the s and p orbitals of the next main shell. for example, electrons in the $3d$ have energy higher than those in the $4 s$ orbital while lower than those of the $4 p$ orbital.

by the aufbau principle, electrons fill orbitals one at a time, starting from those of the lowest energy. the $4s$ orbital is therefore filled right after $3p$ orbitals and before $3 d$ orbitals.

potassium has electron configuration $[\text{ar}] 4 s^{1}$ and calcium $[\text{ar}] 4 s^{2}$ . the s orbital of a main shell holds a maximum of two electrons. the next element would thus have the electron configuration $[\text{ar}] 4 s^{2} \; 3d^{1}$ and satisfy the requirements.

a neutral atom of the element contains three electrons on top of the most recent noble gas element. it should thus be placed in the third column of the periodic table. both scandium and yttrium would satisfy the conditions. an aufbau diagram indicates that the 4f orbital is filled before the 5d. however, it appears that exceptions exists for both lanthanum and actinium. neutral atoms of the two d-block elements also demonstrate the $ns^{2} \; (n-1) p^{1}$ and should be highlighted as well.

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How do you prepare a 250 ml of a 2.35 m hf dilution from a 15.0 m solution...