Chemistry, 07.11.2019 06:31 kaleighashtyn

Calculate the molarity of a solution of ethanol in water in which the mole fraction of ethanol is 0.040(assume the density of water to be one).

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As the given moles OF ethanol = 0.040
now will find water moles that will b
moles of water = 1 - 0.040=0.96 (substract 1 from etahnol mole fraction)
now the
mass of water = 0.96 mol x 18.02 g/mol=17.3 g where 18 is atomic mass of water
mass of ethanol = 0.040 x 46 g/mol =1.84 g
now
mass of solution = 17.3 + 1.84=19.1 g that is mass of water +mass of etanol
Now
assume that the density of the solution = 1g/mL
so the
volume ofsolution = 19.1 mL = 0.0191 L
so finally the molarity will be
M = 0.040/ 0.0191=2.1
hope it helps

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.