Foram encontradas 50 questões.
Para a preparação de uma solução em um balão volumétrico com capacidade de 250 mL adicionaram-se 50 mL de uma solução de nitrato de alumínio, 0,10 mol.L–1 e 25 mL de uma solução de ácido nítrico 0,10 mol.L–1. Completou-se o volume até o traço de aferição com água destilada.
As concentrações, em mol.L–1, dos íons alumínio e nitrato na solução preparada são, respectivamente,
Provas
Dissolveu-se 23,25 g de anilina (C6H5NH2) em água (pH = 7,0) purificada por processo de destilação e deionização. Transferiu-se essa solução quantitativamente para um balão volumétrico de capacidade 1 000 mL e completou-se o volume até o traço de aferição a 25 ºC. O pH da solução final é igual a
Dado:
Constante de Basicidade da anilina a 25 ºC Kb !$ \cong !$ 4 x 10–10
Provas
Preparou-se uma mistura reacional adicionando-se um mol de cloreto de amônio e um mol de carbonato de sódio a um litro de água destilada. Após a solubilização completa dos sais foi atingido o equilíbrio reacional.
Considerando-se as espécies que interagem com a água, após atingido o equilíbrio químico, obteve-se na solução a preponderância da concentração de
Provas
Em um acidente envolvendo incêndio em um laboratório químico ocorreu o vazamento de um frasco de mercúrio, e sua vaporização resultou em uma pressão parcial de mercúrio estimada em 10–1 atm. Considerando-se que a temperatura no momento do acidente atingiu 1200 K, o total de átomos de mercúrio, por litro (átomos . L–1) no ambiente do acidente, era de aproximadamente
Dados:
R = 0,082 atm . L . mol–1 . K–1
Constante de Avogadro 6,0 x 10+23 mol–1
Provas
A teoria dos orbitais moleculares foi a ferramenta teórica que esclareceu o que era observado experimentalmente, quanto ao caráter magnético da molécula de oxigênio. Por meio dessa teoria, pode-se também determinar a ordem de ligação de espécies.
Considerando-se as moléculas de O2, CO e NO, a que apresenta caráter magnético diferente das demais e a que apresenta menor valor de ordem de ligação são, respectivamente,
Provas
De acordo com a norma-padrão da língua portuguesa, assinale a alternativa em que a concordância verbal e/ou nominal está corretamente empregada.
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DIET DRINKS "LINK TO DEPRESSION" QUESTIONED
Experts are questioning whether diet drinks could raise depression risk, after a large study has found a link.
The US research in more than 250,000 people found depression was more common among frequent consumers of artificially sweetened beverages. The work, which will be presented at the American Academy of Neurology’s annual meeting, did not look at the cause for this link.
Drinking coffee was linked with a lower risk of depression.
People who drank four cups a day were 10% less likely to be diagnosed with depression during the 10-year study period than those who drank no coffee. But those who drank four cans or glasses of diet fizzy drinks or artificially sweetened juice a day increased their risk of depression by about a third. Lead researcher Dr Honglei Chen, of the National Institutes of Health in North Carolina, said: “Our research suggests that cutting out or down on sweetened diet drinks or replacing them with unsweetened coffee may naturally help lower your depression risk.”
But he said more studies were needed to explore this. There are many other factors that may be involved. And the findings – in people in their 50s, 60s, 70s and 80s and living in the US – might not apply to other populations. The safety of sweeteners, like aspartame, has been extensively tested by scientists and is assured by regulators.
Gaynor Bussell, of the British Dietetic Association, said: “Sweeteners used to be called ‘artificial’ sweeteners and unfortunately the term ‘artificial’ has evoked suspicion. As a result, sweeteners have been very widely tested and reviewed for safety and the ones on the market have an excellent safety track record. However, the studies on them continue and this one has thrown up a possibly link – not a cause and effect – with depression.”
(http://www.bbc.co.uk/news/health-20943509.09.01.2013. Adaptado)
Provas
Leia o texto para responder a questão.
DIET DRINKS "LINK TO DEPRESSION" QUESTIONED
Experts are questioning whether diet drinks could raise depression risk, after a large study has found a link.
The US research in more than 250,000 people found depression was more common among frequent consumers of artificially sweetened beverages. The work, which will be presented at the American Academy of Neurology’s annual meeting, did not look at the cause for this link.
Drinking coffee was linked with a lower risk of depression.
People who drank four cups a day were 10% less likely to be diagnosed with depression during the 10-year study period than those who drank no coffee. But those who drank four cans or glasses of diet fizzy drinks or artificially sweetened juice a day increased their risk of depression by about a third. Lead researcher Dr Honglei Chen, of the National Institutes of Health in North Carolina, said: “Our research suggests that cutting out or down on sweetened diet drinks or replacing them with unsweetened coffee may naturally help lower your depression risk.”
But he said more studies were needed to explore this. There are many other factors that may be involved. And the findings – in people in their 50s, 60s, 70s and 80s and living in the US – might not apply to other populations. The safety of sweeteners, like aspartame, has been extensively tested by scientists and is assured by regulators.
Gaynor Bussell, of the British Dietetic Association, said: “Sweeteners used to be called ‘artificial’ sweeteners and unfortunately the term ‘artificial’ has evoked suspicion. As a result, sweeteners have been very widely tested and reviewed for safety and the ones on the market have an excellent safety track record. However, the studies on them continue and this one has thrown up a possibly link – not a cause and effect – with depression.”
(http://www.bbc.co.uk/news/health-20943509.09.01.2013. Adaptado)
Provas
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